There must be a leak but can’t think where

[Anj]

Appreciate the advice...

I have attached a schematic of my heating system. Has a 2018 Worcester boiler with a UVC (but the UVC could be older not sure when that was installed, I do know the previous Viessmann boiler had failed). There a couple of motorised valves for the heating and hot water.

The problem is that the pressure in the system (as read from 2 gauges on the pipe work) keeps falling (overnight 1.5bar to 1.2bar even with the boiler off and isolated).

So I have tried to isolate as best as I can and closed off gate valves to the rads (see picture) downstairs but I can see that given the position of the valves I can’t isolate the upstairs rads (unless I add a gate valve). But I can’t see any water from upstairs (the ceiling would have caved by now).

With the boiler off and isolated and the downstairs rads isolated the only thing that was on last night was the immersion heater in the tank. The heating control was on but could only have moved the motorised valve the boiler was off so nothing else. Was sure the leak was in the rads downstairs and so totally expected the pressure to have stayed at 1.5 as the rads were isolated but no, the pressure still fell.

The expansion tank has air (quick press of the Schrader valve).

None of the PRV drain lines have any water (bone dry).

There are two gauges (no idea why) but they both read the same so not a faulty gauge.

Is it possible the UVC is leaking? Can that ever happen... the mains pressure seems to be OK and I would have thought that the mains pressure (3 bar?) would prevent the heating coil (1.5 bar) from leaking?

Any suggestion for next steps? Should I drain the system and add the extra gate valve to isolate upstairs (even though I can’t believe it is that)?

All the tank/boiler valves are in the garage exposed so no chance of a leak being missed.

Really puzzled. Am hoping those with experience on UVC (I am not a plumber) can advise?

 

[moonlight]

When you heating is on the pressure will increase say to 1.5 bar for the sake of this issue, when you heating is off the pressure will drop to its cold state say 1.2 bar this is quite normal. If your pressure continued to drop there would be another issue that would need investigating. Hope this helps.

 

[Anj]

When you heating is on the pressure will increase say to 1.5 bar for the sake of this issue, when you heating is off the pressure will drop to its cold state say 1.2 bar this is quite normal. If your pressure continued to drop there would be another issue that would need investigating. Hope this helps.

Thanks for the speedy response

i don’t think that’s it
When it’s cold I charge it to 1.5 bar. When it gets hot it goes up to 1.75ish.
When it cools it falls below 1.5.

Ive repeated this starting at 1.3 bar when cold (hoping that the leak might be small at a lower pressure). It goes up to 1.5/1.6 then again falls below 1.3 when cold.

If I leave it for longer it goes down to 1bar... I haven’t let it go below that.

 

[moonlight]

Can you isolate the under floor and check over night?

 

[John.g]

Would suggest checking the EV pre charge air pressure, if this has been set too high then even the slightest change in temp will have a very big effect on the pressure as water is incompressible. When next the pressure falls to 1 bar, get a tyre pressure gauge and check the air end pressure, if that is > 1.0 bar, say 1.5 bar, then that just might be the problem and very easy to check without EV drain down.
Another clue to ~ 1.5 pre charge pressure is if it re pressurises almost instantly from 1.0 bar to 1.5 bar when topping up.

 

[Anj]

Can you isolate the under floor and check over night?

Yes I did that. Was surprised to see the pressure fall from 1.5 to 1.2 with the underfloor isolated overnight.

I had thought the leak was there but I guess not. The gate valves do work (as I had used them when the system was on and they did stop all the rads getting warm) so I don’t think the valves are letting by either.
[automerge]1586345644[/automerge]

Would suggest checking the EV pre charge air pressure, if this has been set too high then even the slightest change in temp will have a very big effect on the pressure as water is incompressible. When next the pressure falls to 1 bar, get a tyre pressure gauge and check the air end pressure, if that is > 1.0 bar, say 1.5 bar, then that just might be the problem and very easy to check without EV drain down.
Another clue to ~ 1.5 pre charge pressure is if it re pressurises almost instantly from 1.0 bar to 1.5 bar when topping up.

Oh... thanks ... good one. Will definitely do that.

I don’t have an isolation valve to the EV so I will wait for the pressure to get to 1bar and then check the EV and report back. I assume the pressure under the diaphragm should be the same as that above the diaphragm? Is that what you are saying?

Thanks!

 

[John.g]

Yes.------(message must be Twenty characters)

 

[Scott_D]

What boiler do you have?
Any AAVs?
If you leave it for a few days does it continue to drop?

 

[Anj]

What boiler do you have?
Any AAVs?
If you leave it for a few days does it continue to drop?

No other AAV other than the one that was in the boiler
— it’s a Worcester 40CDi Classic Regular


edit: Sorry need to add it does continue to fall if the system is running but I’ve never let it go below 1bar.

 

[karltheplumber]

When was the boiler last serviced? Common problem is the AAV (automatic air vent/bleed) doesn't seal properly causing water to escape within the casing.
Ive also had a hairline crack inside the heat exchanger which was leaking down the condense pipe and loosing pressure.
have you had an engineer look into the issue?

 

[moonlight]

If you isolated the underfloor and no leaks, and also the boiler with no leaks have you checked the expansion vessel, if its dropping while you are using the heating it should be easier to find. Have you looked at the pressure relief pipework outside?

 

[Anj]

If you isolated the underfloor and no leaks, and also the boiler with no leaks have you checked the expansion vessel, if its dropping while you are using the heating it should be easier to find. Have you looked at the pressure relief pipework outside?

Thanks for the suggestion.

Just to be clear I isolated the underfloor and the boiler from the pressure gauges but the pressure gauges still go down.

I agree there only seems to be the UVC and the EV (and the upstairs rads) that are now effectively linked to the pressure gauges. I’ve checked the EV by pressing the schrader valve (only for a second - is that enough?) and air came out. Is that the only test for an EV?

The PRVs (there is one near the EV and one at the UCV) are both in the garage (I know that’s against the regs (dodgy installer I guess) but the pipe terminates just above the floor /at the floor level). Both are bone dry... I did put a balloon on the end of the UCV PRV pipe even though there would be a wet patch on the garage floor and nothing has come out. The pressure is falling with everything switched off (ie no heating)

Any chance the UCV could be leaking internally? or is that physically not possible?

 

[moonlight]

If you are loosing that amount of water and you have isolated the underfloor, by the way did you isolate the underfloor near the manifold? You have said there is no water from the PRV's pipework, you must by now have visible damp.
If you keep letting air out of the expansion vessel, you will have another problem. The expansion vessel will have a label with the amount of pressure that should be in the vessel, you might have to put some air in it. When the gauge is at the bottom or no reading pump air into the vessel to the manufactures guide on the label as you have an external expansion vessel it will possibly be more than you think so check the label.

Close all the radiator valves both ends and isolate the underfloor that would eliminate the radiators too and check overnight.

 

[Anj]

If you are loosing that amount of water and you have isolated the underfloor, by the way did you isolate the underfloor near the manifold? You have said there is no water from the PRV's pipework, you must by now have visible damp.
If you keep letting air out of the expansion vessel, you will have another problem. The expansion vessel will have a label with the amount of pressure that should be in the vessel, you might have to put some air in it. When the gauge is at the bottom or no reading pump air into the vessel to the manufactures guide on the label as you have an external expansion vessel it will possibly be more than you think so check the label.

Close all the radiator valves both ends and isolate the underfloor that would eliminate the radiators too and check overnight.

so the “underfloor” is just the central heating heating pipes under the screed there is not water UFH. There are two gate valves (flow and return) in the garage just before the pipes disappear into the wall and then into the screed of the kitchen on the other side of the wall. It’s just these two gate valves I have used to isolate the pipes in the screed (no manifold).

I agree for that much water loss I should see the water somewhere and I can’t. Driving me bananas...

so either:
1. The gate valves to the pipes in the screed are letting by and there is a leak under the screed... but when I ran the system hot with closed gate valves the small part of the pipes on the other side of the valve (before the wall) were not hot and none of the rads in kitchen were warm so I think the valves are OK
2, the valves to the boiler are letting by and there is a leak in the combustion chamber leaking into the condensate line... I am going close two more valves (above the pump (flow) and the magnafilter (return) just in case
3. One person here has indicated that the EV might be overcharged and so temperature is causing the issue (I’ll check the EV pressure). I don’t recall seeing a label but will take a better look in the morning. But I thought if the EV was the issue then I’d see water either at the schrader valve or the PRV ? Anywhere else to check?
4. I can add another gate valve to isolate the upstairs (and drop down rads) but if the leak was there then I’d have seen that water somewhere in the ceiling by now for sure if it was leaking that much.
5. The only thing left is the UVC - but Im not even sure that can leak internally?

Reallly appreciate the help!

 

[John.g]

Just to clarify re EV. (a bit long winded)

"Normal" would/could be a EV with a pre charge air pressure of 1.0 bar which is then pressurised (filling pressure) to 1.5 bar with system cold. A 12 litre EV at these conditions will then contain 2.4 litres of water (known as the reserve). Each time the system heats up then the expanded water will enter the EV and add to the 2.4 litres so the EV pressure will increase, example, a system of total vol 85 litres heated to average of (flow/return) 65C will expand and add a further 1.6 litres to the EV resulting in a final pressure of 1.98 bar. On cooling down, the EV pressure will reduce to its original 1.5 bar and its 2.4 litre water reserve. If there are any leaks in the system, then 2.4 litres (the reserve) will have to leak until the pressure falls to its pre charge pressure of 1.0 bar. Normally, with no leakage but allowing for occasional air venting, this reserve will last for at least a year (or even years) without top up.
Now, suppose the EV was pre charged to 1.5 bar and was prefilled to 1.5 bar then there is no water reserve and the final pressure after system heat up will be 1.87 bar and on cool down will be 1.5 bar but if there is even the tiniest of leaks then the pressure will fall very rapidly below 1.5 bar as there is no water reserve. That is why its so important and it's relatively easy to check that pre charge pressure.

 

[Anj]

Just to clarify re EV. (a bit long winded)

"Normal" would/could be a EV with a pre charge air pressure of 1.0 bar which is then pressurised (filling pressure) to 1.5 bar with system cold. A 12 litre EV at these conditions will then contain 2.4 litres of water (known as the reserve). Each time the system heats up then the expanded water will enter the EV and add to the 2.4 litres so the EV pressure will increase, example, a system of total vol 85 litres heated to average of (flow/return) 65C will expand and add a further 1.6 litres to the EV resulting in a final pressure of 1.98 bar. On cooling down, the EV pressure will reduce to its original 1.5 bar and its 2.4 litre water reserve. If there are any leaks in the system, then 2.4 litres (the reserve) will have to leak until the pressure falls to its pre charge pressure of 1.0 bar. Normally, with no leakage but allowing for occasional air venting, this reserve will last for at least a year (or even years) without top up.
Now, suppose the EV was pre charged to 1.5 bar and was prefilled to 1.5 bar then there is no water reserve and the final pressure after system heat up will be 1.87 bar and on cool down will be 1.5 bar but if there is even the tiniest of leaks then the pressure will fall very rapidly below 1.5 bar as there is no water reserve. That is why its so important and it's relatively easy to check that pre charge pressure.

Thanks that explanation is quite helpful for me. I’ll let the system pressure fall away (or drain it) as i don’t have an iso valve to the EV and check it.

 

[John.g]

Yes, and as the pressure is decaying then check the air end pressure frequently and when (or if) the system pressure falls below the air end pressure then that will give you a very good indication of the air end pressure but would also advise checking both pressures at 1.5 bar or greater when hot just to ensure that both are equal. Also remember to take the differences in elevation between the EV and the system pressure gauge, if the EV is the lower (elevation) of the two then the air end pressure corrected to system pressure is air end pressure - 0.1bar for every 1M of elevation and +0.1bar if EV is the higher of the two.

 

[Anj]

Yes, and as the pressure is decaying then check the air end pressure frequently and when (or if) the system pressure falls below the air end pressure then that will give you a very good indication of the air end pressure but would also advise checking both pressures at 1.5 bar or greater when hot just to ensure that both are equal. Also remember to take the differences in elevation between the EV and the system pressure gauge, if the EV is the lower (elevation) of the two then the air end pressure corrected to system pressure is air end pressure - 0.1bar for every 1M of elevation and +0.1bar if EV is the higher of the two.

Thanks for the detailed responses.
The EV label says Precharge 1.5 bar.
The system is at 1.2 bar right now
I attached a tyre pressure gauge to the EV and it also reads 1.2 bar... hmmm not conclusive yet but possible little charge in the EV?

I will monitor both today/tonight (I might have to dump the system pressure to get the true reading in the EV)

the odd part then ... if the EV has no charge then the water must be going somewhere (or do I have that wrong?
If not out the PRV lines they are bone dry (the system has never gone to three bar and right now the system is cold and losing pressure)

 

[John.g]

Theoretically, if the precharge pressure fell to 0 Bar and with a filling pressure of 1.5 bar then the final pressure would be ~ 2.7 bar, close to PRV limit but I don't think you observed any pressures approaching this. If the precharge pressure was 1.5 bar originally and the system was filled to 1.5 bar then no reserve and frequent top ups. IMO, the precharge pressure should be 0.8/1.0 bar and fill pressure 1.3/1.5 bar to avoid excessive final pressure.
You will have to get a differential pressure of ~ 0.2/0.3 between EV/system pressure before you can get a good feel for the present EV pressure. Once you know that then you can see your next step(s).

 

[gpbeck]

If they really are gate valves they almost always let by a bit because of design. Though not enough to warm radiators.

 

[Anj]

Thanks for the detailed responses.
The EV label says Precharge 1.5 bar.
The system is at 1.2 bar right now
I attached a tyre pressure gauge to the EV and it also reads 1.2 bar... hmmm not conclusive yet but possible little charge in the EV?

I will monitor both today/tonight (I might have to dump the system pressure to get the true reading in the EV)

the odd part then . if the EV has no charge then the water must be going somewhere (or do I have that wrong?
If not out the PRV lines they are bone dry (the system has never gone to three bar and right now the system is cold and losing pressure)

It’s not possible there is a

1. If they really are gate valves they almost always let by a bit because of design. Though not enough to warm radiators.

ok
I couldn’t feel any heat on the pipe either just downstream of the valve.

But there is a drain cock on the other side of the gate valve for the downstairs loop.
If I open the drain cock then the pressure should fall away in the downstairs loop and I should see the pressure drop dramatically upstream of the valve if it is letting by? If the pressure doesn’t change upstream of the valve then can I assume it is holding?

 

[John.g]

You also mentioned maybe a leaking boiler even though you closed the isol valves, when you have completed your present test and precharge and refill the system, suggest you raise to 2.5 bar cold, remove (if you cannot see drain) a piece of the condensate pipe and see if any leakage through here.

 

[Anj]

You also mentioned maybe a leaking boiler even though you closed the isol valves, when you have completed your present test and precharge and refill the system, suggest you raise to 2.5 bar cold, remove (if you cannot see drain) a piece of the condensate pipe and see if any leakage through here.

Right I waited a couple of days with all the valves closed (boiler isolated), downstairs isolated. The pressure didn’t fall below 1.2bar.

Then I opened a joint in the condensate line recharged to 1.5 to see if anything came out. Nothing. System fell a little but not much.

So I decided to bleed the system but I wanted to check the gate valves so I opened the drain cock on the downstairs loop with the Gate valves for the downstairs closed (and all the rads closed as well as suggested by someone on here). Hardly any water came out despite me full opening the drain cock.
A little dribble started and continued for 1/2 hour Which I assume came from the downstairs loop as the drain cock is actually about level with the loop in the downstairs screed. (I figured if the gate valves were letting by I would see a lot water and pressure drop as the drain cock is right next to Gate valve).

I think the gate valves are doing their job so after that I opened the Gate valve in the return and drained the system.

The EV pressure (now i have put a tyre gauge on it) fell to zero! I feel like a muppet for not checking the obvious. I think the puff of air I was seeing when I pushed the valve (for a split second) was perhaps the last few puffs of air the EV had....

But I still don’t understand - none of the PRV have opened so can’t understand why the pressure was falling.
Also John G you say “if the precharge pressure fell to 0 Bar and with a filling pressure of 1.5 bar then the final pressure would be ~ 2.7 bar”.
Would you mind explaining how so? I don’t understand that.. I thought if I see 1.5 bar on the gauge the whole system is at 1.5 bar ?
I used be to an electrical engineer (sorry) so I am OK with maths but am not so familiar with hydraulics.

Anyway I am checking the EV, pressurised it to 18psi/1.25 bar to see if it holds. I will then lower this to 1 bar as suggested by John.G and then fill the system back up, monitoring both the system and EV pressure.

Thanks for the help so far.

 

[John.g]

I should have explained it a bit better, your understanding of the 0 bar pre charge would be the most likely (by far) so we will use that in the first case, if the pre charge and filling pressures were 1.5 bar and assume a leak at the air end, then as it falls the system will require topping up and the final pressure (when hot) will start rising as well, eventually rising to 3.0 bar causing the PRV to lift, if you had installed the EV with 0 pressure and if the bladder was hard up against the air end then the effect is the same as a holed bladder (or having no EV installed) and the PRV will lift almost as soon as the system starts heating.
My calculation was based on the bladder being hard up against the water end with the pre charge pressure reduced to 0 (very unlikely unless the air had leaked away before installation or some one had reduced it to zero (again very unlikely), under these conditions and with a filling pressure of 1.5 bar then the filling volume will be 7.2 litres and final pressure (at both ends) will be ~ 2.7 bar, so every time the the pressure fell to 1.0 bar (your topping up pressure limit) and with a filling pressure of 1.5 bar then the filling volume will be 2.4 litres and final pressure (at both ends) will be ~ 2.7 bar, so you would have lost ~ 2.4 litres of water (at each top up) which hopefully seems most unlikely.

 

[Anj]

I should have explained it a bit better, your understanding of the 0 bar pre charge would be the most likely (by far) so we will use that in the first case, if the pre charge and filling pressures were 1.5 bar and assume a leak at the air end, then as it falls the system will require topping up and the final pressure (when hot) will start rising as well, eventually rising to 3.0 bar causing the PRV to lift, if you had installed the EV with 0 pressure and if the bladder was hard up against the air end then the effect is the same as a holed bladder (or having no EV installed) and the PRV will lift almost as soon as the system starts heating.
My calculation was based on the bladder being hard up against the water end with the pre charge pressure reduced to 0 (very unlikely unless the air had leaked away before installation or some one had reduced it to zero (again very unlikely), under these conditions and with a filling pressure of 1.5 bar then the filling volume will be 7.2 litres and final pressure (at both ends) will be ~ 2.7 bar, so every time the the pressure fell to 1.0 bar (your topping up pressure limit) and with a filling pressure of 1.5 bar then the filling volume will be 2.4 litres and final pressure (at both ends) will be ~ 2.7 bar, so you would have lost ~ 2.4 litres of water (at each top up) which hopefully seems most unlikely.

Thanks John
the EV is a red Zilmet unit which states 35l on it built in 2018. Am not sure how it loses all the charge unless the valve is failing(?).
No PRV has let by so maybe the small amount of air has saved me. I’ve left it charged at 1.2bar and will leave it overnight. If it holds then I’ll lower it to one bar and charge the system to 1.2bar so should see the air side go up to 1.2bar?

I think I understand the first scenario...just to check - the 3.0 bar you refer to is assuming the incoming mains pressure is 3.0 bar?

as to the second how did you calculate the filling volume is 7.2l (what is the equation/formula?) Does the size of the EV make a difference? So you are saying 2.4l charge results in 0.5 bar pressure increase? Is the 2.7bar you refer to the proxy for mains pressure.

thanks for your patience with a non plumber!

 

[SJB060685]

Its worth pointing out an absolute pressure gauge used in sealed systems with have different readings depending on where its installed

 

[Anj]

Its worth pointing out an absolute pressure gauge used in sealed systems with have different readings depending on where its installed

The pressure gauge is installed right next to the EV (in fact there are two gauges both next to the EV) I suppose that takes away the height issue.

 

[John.g]

Thanks John
the EV is a red Zilmet unit which states 35l on it built in 2018. Am not sure how it loses all the charge unless the valve is failing(?).
No PRV has let by so maybe the small amount of air has saved me. I’ve left it charged at 1.2bar and will leave it overnight. If it holds then I’ll lower it to one bar and charge the system to 1.2bar so should see the air side go up to 1.2bar?

I think I understand the first scenario...just to check - the 3.0 bar you refer to is assuming the incoming mains pressure is 3.0 bar?

as to the second how did you calculate the filling volume is 7.2l (what is the equation/formula?) Does the size of the EV make a difference? So you are saying 2.4l charge results in 0.5 bar pressure increase? Is the 2.7bar you refer to the proxy for mains pressure.

thanks for your patience with a non plumber!

OK, since we now know the EV has a capacity of 35 litres we will start from scratch and just to state that the mains pressure has nothing to do with the pressure rise, you only need sufficient mains pressure to give you the required filling pressure.


(Rem below that absolute pressure = gauge pressure +1)
Assume that the EV has a pre charge pressure of 1 bar and a filling pressure of 1.5 bar.
Now because with a gas/air, vol is inversely proportional to (absolute) pressure then the vol of air after filling to that 1.5 bar will be (35* 2/2.5) or 28 litres so the EV will now contain (35-28) 7 litres of water, now just assume that your heating system volume is 100 litres which will expand by 1.83% when heated to a average of 65C (flow+return)/2) which equals to a expanded vol of (100*1.83%) 1.83 litres, this expanded vol will now enter the EV so the EV will now contain (7+1.83) 8.83 litres (water) and the air end, (35-8.83) 26.17 litres, from this then the pressure now in the EV will be (2.5*28/26.17) 2.67 bar.abs or 1.67 bar(G) the pressure you see on your pressure gauge.
So the EV pressure will vary between cold and hot from 1.5 bar to 1.67 bar. (This might seem a very small pressure rise but you have a huge EV) Obviously if your system vol is greater that 100 litres then the final pressure will be greater and will be less with a smaller vol.

Now if the EV develops a leak at the air end probably through the Schrader valve or its seal, then the air volume will gradually start decreasing and eventually the EV will be almost full of water and the pressure will increase gradually due to expansion and reduced air end vol until eventually the PRV lifts at 3 bar. what it means in effect that you would have topped up by ~ 20 litres, not because of any system leak but because of a EV air leak.
I won't go any further at the moment, see what your test shows, but if no drop in pressure then suggest 1.0 pre charge pressure and 1.5 bar filling pressure which will give a reserve of 7 litres which will mean no top ups required for "years" (if no leaks of course).
You can do your calculations in the attached excel sheet.

 

[SJB060685]

John I was just pointing out that different types of pressure gauges are used depending on the situation. An absolute pressure gauge used in a sealed system takes absolute zero as a reference point, whereas a vented gauge takes surrounding atmospheric pressure as its reference point, obviously if atmospheric pressure changes then so will gauge reading.

 

[John.g]

Right I waited a couple of days with all the valves closed (boiler isolated), downstairs isolated. The pressure didn’t fall below 1.2bar.

Then I opened a joint in the condensate line recharged to 1.5 to see if anything came out. Nothing. System fell a little but not much.

So I decided to bleed the system but I wanted to check the gate valves so I opened the drain cock on the downstairs loop with the Gate valves for the downstairs closed (and all the rads closed as well as suggested by someone on here). Hardly any water came out despite me full opening the drain cock.
A little dribble started and continued for 1/2 hour Which I assume came from the downstairs loop as the drain cock is actually about level with the loop in the downstairs screed. (I figured if the gate valves were letting by I would see a lot water and pressure drop as the drain cock is right next to Gate valve).

I think the gate valves are doing their job so after that I opened the Gate valve in the return and drained the system.

The EV pressure (now i have put a tyre gauge on it) fell to zero! I feel like a muppet for not checking the obvious. I think the puff of air I was seeing when I pushed the valve (for a split second) was perhaps the last few puffs of air the EV had..

But I still don’t understand - none of the PRV have opened so can’t understand why the pressure was falling.
Also John G you say “if the precharge pressure fell to 0 Bar and with a filling pressure of 1.5 bar then the final pressure would be ~ 2.7 bar”.
Would you mind explaining how so? I don’t understand that.. I thought if I see 1.5 bar on the gauge the whole system is at 1.5 bar ?
I used be to an electrical engineer (sorry) so I am OK with maths but am not so familiar with hydraulics.

Anyway I am checking the EV, pressurised it to 18psi/1.25 bar to see if it holds. I will then lower this to 1 bar as suggested by John.G and then fill the system back up, monitoring both the system and EV pressure.

Thanks for the help so far.

Just to clear up a few other items...
“if the precharge pressure fell to 0 Bar and with a filling pressure of 1.5 bar then the final pressure would be ~ 2.7 bar”.
Would you mind explaining how so? I don’t understand that.. I thought if I see 1.5 bar on the gauge the whole system is at 1.5 bar ?"
The "final pressue" refers to the pressure after the system heats up again and would have been 2.7 bar with a 12 litre EV but only 1.67 bar with that 35 litre EV.

Re: now no air pressure at the air end....I calculate that the final pressure would be approaching 3 bar when there is still 6 litres of air in the EV so how it reached 0 pressure without lifting the PRV is beyond me except that the air leakage is/was so bad that it was leaking faster than the water expansion while heating up, very strange, but the test will tell alot.

 

[Anj]

John.G
Thank you thank you thank you.
I now understand the calcs (Boyles Law) I missed the Gauge v Absolute pressure part.

I have 21 rads but 9 are very small/towel rads so I think a system volume of about 150 litres. When the system was running fine it would go from 1.5bar(G) to 1.75bar(G) which according to the calcs is spot on.

Anyway the EV didn’t lose any volume overnight but stupidly I left the tyre gauge connected which might have stopped the leak if it was from the needle area, so I will repeat the test. I put some soapy water on the valve but no bubbles showed.

As for the PRV not releasing I now realise there is only one PRV for the CH system the other seems to be a pressure equalisation valve on the incoming water main and the other is on the HW cylinder. I think the latter two have nothing to do with the CH system. It might be that the PRV on the CH system (right under the EV) is jammed/doesn’t work - I haven’t tested it.
Maybe I should test it when I next pressure the system? - I have heard sometimes they don’t reseat and then leak but on balance better to know it is working. I think it must be installed with the tank and boiler in 2018 so it would be surprising if it has failed.

One question though as the EV had lost all its charge then wont this just happen again(?) hard to believe the leak will seal itself?
I guess if I see another pressure drop then the first thing to do is drain the system and check the EV and then replace it if it’s lost charge again.

I’ll redo the dry EV test and the pressure the system and see what happens.

 

[John.g]

That's all you can do, you will have to rule out the EV one way or the other before harbouring any suspicions that it still might be a system leak. The whole thing is a bit mysterious to say the least, as you say, if there is no leak at the air end then how did the pressure fall to zero because in doing so, with your constant top ups to 1.5 bar, it should have reached 3.0 bar on heat up when the air end vol fell to ~ 9 litres. The only other (unlikely) scenario that fits is that the EV pre charge pressure had lost its pressure before install (with bladder at water end), if that was the case then the final pressure would have been > 2 bar on heat up and to fit your observed pressure of 1.75 bar would mean a system contents of ~ only 75 Litres.

I presume your boiler is a regular boiler with external pump?, if its a system boiler then it will also have its own EV & PRV venting outside the building but that external EV may have been fitted if the system vol is large, even if not a system boiler it may still have a PRV, any GSR on here can tell you that if you post the make/model.
Edit: I see its a Worcester 40CDi Classic Regular so doesn't seem to have a PRV.

 

[Anj]

That's all you can do, you will have to rule out the EV one way or the other before harbouring any suspicions that it still might be a system leak. The whole thing is a bit mysterious to say the least, as you say, if there is no leak at the air end then how did the pressure fall to zero because in doing so, with your constant top ups to 1.5 bar, it should have reached 3.0 bar on heat up when the air end vol fell to ~ 9 litres. The only other (unlikely) scenario that fits is that the EV pre charge pressure had lost its pressure before install (with bladder at water end), if that was the case then the final pressure would have been > 2 bar on heat up and to fit your observed pressure of 1.75 bar would mean a system contents of ~ only 75 Litres.

I presume your boiler is a regular boiler with external pump?, if its a system boiler then it will also have its own EV & PRV venting outside the building but that external EV may have been fitted if the system vol is large, even if not a system boiler it may still have a PRV, any 'Registered Professional Gas Engineer' on here can tell you that if you post the make/model.

Thanks John
The boiler is a Worcester Greenstar 40CDi Regular

It has an external pump and am pretty sure no PRV (I couldn’t see one on the manual diagram) however it can dump water direct to the condensate line through a manual valve so maybe there is another safety valve I can’t see.

 

[Anj]

Thanks John
The boiler is a Worcester Greenstar 40CDi Regular

It has an external pump and am pretty sure no PRV (I couldn’t see one on the manual diagram) however it can dump water direct to the condensate line through a manual valve so maybe there is another safety valve I can’t see.

John.G
So the EV lost 2psi (18psi to 16psi) in a day (psi better scale on the tyre gauge) even without the system being pressured (the tyre gauge was disconnected this time).
I have ordered a new EV - will report back in a couple of days once it is installed.

thanks once again for the help.