Automatic Bypass Valve Query

[Tigermad]

I had an automatic bypass valve fitted to my unvented system yesterday and it was left at 0.4. Goes from 0.1-0.5. Anyhow I thought I would set it today according to the instructions. So I closed it off completely to th 0.5 mark and then turned all the trvs on. I then began turning it until the pipe started to get warm. Problem is the abv is in the airing cupboard and it is fitted to the pipes marked flow and return. The flow pipe is hot but the return pipe remains stone cold. Even after leaving the heating on for 10 minutes. So turning the valve makes no difference. Am I doing something wrong? Why is the return pipe stone cold?
I just tried turning the heating off and the pipe from the ABV got red hot even though the ABV is turned off

Ignore the non copper pipes. These are from the old system and are redundant.

 

[Aire]

I presume the pipe to the zone valve is the flow? If it is then the abv looks to fitted the wrong way.

Is the abv fitted before or after the zone valve?

 

[Tigermad]

I presume the pipe to the zone valve is the flow? If it is then the abv looks to fitted the wrong way.

Do you mean the horizontal one? The horizontal one is coming downhill from the flow to return. Is this wrong? The return is on the left of the bypass and the flow is on the top (horizontal), the one with the arrow. The zone valve is attached to the return.
The unvented hot water cylinder is in the loft so the abv is before the zone valve from the boiler but after the zone valve coming down from the cylinder.

 

[SimonG]

I presume the pipe to the zone valve is the flow? If it is then the abv looks to fitted the wrong way.

Is the abv fitted before or after the zone valve?

Glad it wasn't just me. Thought I'd had too much beer last night.

 

[Tigermad]

So is it right or wrong after my reply?

 

[Aire]

Sounds like it's fitted ok, unless the valve is faulty or blocked then you shouldn't have any issues setting it up.

 

[Tigermad]

So which pipe do I have to feel getting warmer. The very small piece on the left going to the return?

 

[John.g]

I had an automatic bypass valve fitted to my unvented system yesterday and it was left at 0.4. Goes from 0.1-0.5. Anyhow I thought I would set it today according to the instructions. So I closed it off completely to th 0.5 mark and then turned all the trvs on. I then began turning it until the pipe started to get warm. Problem is the abv is in the airing cupboard and it is fitted to the pipes marked flow and return. The flow pipe is hot but the return pipe remains stone cold. Even after leaving the heating on for 10 minutes. So turning the valve makes no difference. Am I doing something wrong? Why is the return pipe stone cold?
I just tried turning the heating off and the pipe from the ABV got red hot even though the ABV is turned off

Ignore the non copper pipes. These are from the old system and are redundant.

View attachment 36343
View attachment 36344

I had an automatic bypass valve fitted to my unvented system yesterday and it was left at 0.4. Goes from 0.1-0.5. Anyhow I thought I would set it today according to the instructions. So I closed it off completely to th 0.5 mark and then turned all the trvs on. I then began turning it until the pipe started to get warm. Problem is the abv is in the airing cupboard and it is fitted to the pipes marked flow and return. The flow pipe is hot but the return pipe remains stone cold. Even after leaving the heating on for 10 minutes. So turning the valve makes no difference. Am I doing something wrong? Why is the return pipe stone cold?
I just tried turning the heating off and the pipe from the ABV got red hot even though the ABV is turned off

Ignore the non copper pipes. These are from the old system and are redundant.

View attachment 36343
View attachment 36344

The 0.1 to 0.5 settings are 0.1 bar to 0.5 bar or 1 M (meter) to 5 m.
The purpose of the ABV is to to maintain a minimum flow rate through the boiler on pump over run and also to maintain a minimum flow rate in the event of a very low heat demand where some/all of the TRVs are throttled in.
I presume that you were just testing its functionality with the above test with all TRVs ON (open??) and a setting of 1 M (0.1). Now the circ pump, depending on its speed setting may or may not be producing 1 M head with a large flow rate (all TRVs open) so you may not have got any flow rate due to this (pump head < 1 M) and maybe a circ pump speed setting of only 1?.
You could look at the pump make/model & current speed setting, then assuming that you need say 0.3 M3 per hour flowrate, by looking at the pump speed curves you can see what pump head is required, for example if the speed setting is 2 then the pump head at this speed required might be 3M so you would set the ABV to 0.3, and so on, you can then test it by shutting off the TRVs and ensure it is then opening.

 

[John.g]

Here is a example of one ABV setting.

 

[Tigermad]

Hi folks me again. Something is not right since the bypass has been fitted. Nearly every night at 6.40pm there a crackling /gushing water sound through the lounge radiator valve. This rad is nearest to the boiler. I have the hot water cylinder programmed on my evohome system to turn off at 6.40pm so I think it’s linked to this. Any ideas why this is happening?

 

[Harvest Fields]

Air? Valve not quite open enough?

 

[Chuck]

Hi folks me again. Something is not right since the bypass has been fitted. Nearly every night at 6.40pm there a crackling /gushing water sound through the lounge radiator valve. This rad is nearest to the boiler. I have the hot water cylinder programmed on my evohome system to turn off at 6.40pm so I think it’s linked to this. Any ideas why this is happening?

At 1839 the boiler is blasting away and the pump is pumping lots of hot water around the DHW loop though the cylinder.

At 1840 and 0 seconds the HW zone valve slams shut but the pump and boiler don't instantly respond so the water flows (fast) round the path of least resistance, which is either the radiator circuit or the ABV depending on how it is set.

By 1840 and 30 seconds the boiler power has been cut back and the pump has adapted to the new conditions and order is restored again.

The problem with ABVs is that they detect and act on pressure differences, which are only indirectly related to the flow rate in a system with TRV's and/or a smart pump. ABVs work pretty well with 'dumb' (constant displacement rate) pumps but not so well with 'smart' (constant pressure) pumps.

To further complicate the story, the purpose of an external ABV has changed over the years. Originally it was an energy-saving refinement to a traditional 'bypass radiator' that was always on ensure a minimum flow rate through the boiler. These days this is not usually needed but ABVs are often still used to to ensure that there is sufficient heat capacity in the circulating circulating water to avoid heat-stress damaging the heat exchanger. Some boilers, typically ones with robust stainless steel heat exchangers don't require an external ABV. Others, particularly ones with aluminium heat exchangers and low water volumes, require not just an ABV but also a minimum loop volume connecting it to the boiler.

As always, the installer needs to read the manufacturer's installation instructions carefully and follow them to the letter.

 

[Tigermad]

At 1839 the boiler is blasting away and the pump is pumping lots of hot water around the DHW loop though the cylinder.
At 1840 and 0 seconds the HW zone valve slams shut but the pump and boiler don't instantly respond so the water flows (fast) round the path of least resistance, which is either the radiator circuit or the ABV depending on how it is set.

The problem with ABVs is that they detect and act on pressure differences which are only indirectly related to the flow rate. They work pretty well with 'dumb' (constant displacement rate) pumps but not so well with 'smart' (constant pressure) pumps.

To further complicate the story, the purpose of an external ABV has changed over the years. Originally it was to ensure a minimum flow rate throuh the boiler but these days it is often to to ensure that there is sufficient heat capacity in the circulating circulating water to avoid heat-stress damaging the heat exchanger. Some boilers, typically ones with robust stainless steel heat exchangers don't require an external ABV. Others, particularly ones with aluminium heat exchangers and low water volumes, require not just an ABV but also a minimum loop volume connecting it to the boiler.

As always, the installer needs to read the manufacturer's installation instructions carefully and follow them to the letter.

Thanks. The radiator noise was better before the bypass was fitted. Can I disable it by fully opening it?

 

[Tigermad]

Air? Valve not quite open enough?

No air in the system because I have tried to bleed all rads a few times now. Although the towel rail upstairs needs constant bleeding and i guess it’s the last rad on the circuit and something weird happens with it. But this thing with the towel rail was happening before the bypass was fitted.

Do you mean the valve on the rad or bypass? The noise is mainly on the left hand side of the radiator as the water goes in.

 

[John.g]

Thanks. The radiator noise was better before the bypass was fitted. Can I disable it by fully opening it?

You disable it by fully closing it, did you ever establish if it is in fact fitted correctly by opening it fully while the boiler is firing normally, you should then feel both flow and return pipes very hot.

 

[Harvest Fields]

Yes on the rad, also you may have mentioned this already but what setting is the pump on?

 

[Tigermad]

You disable it by fully closing it, did you ever establish if it is in fact fitted correctly by opening it fully while the boiler is firing normally, you should then feel both flow and return pipes very hot.

Yes. The pipes eventually got hot. Think I was doing something wrong when checking it. So if I completely close it I can see if the noise gets better without it?

 

[Tigermad]

Yes on the rad, also you may have mentioned this already but what setting is the pump on?

I have tried opening the lock shield valve a bit and closing it but made no difference whilst the noise was happening. The pump is built in to the boiler and it can run on either 70 percent or 100 percent. It’s on the default of 70 percent.

 

[Chuck]

Thanks. The radiator noise was better before the bypass was fitted. Can I disable it by fully opening it?

No. Don't "fully open" it. It should be set to operate at the highest pressure difference that allows it to achieve its intended purpose.

If you are determined to play around open it by small amounts, say quarter turns until it reduces the 1840 noise. But, if you open it enough to completely eliminate the 1840 noise you'll probably have gone too far and have replaced one problem with another.

 

[Tigermad]

No. Don't "fully open" it. It should be set to operate at the highest pressure difference that allows it to achieve its intended purpose.

If you are determined to play around open it by small amounts, say quarter turns until it reduces the 1840 noise. But, if you open it enough to completely eliminate the 1840 noise you'll probably have gone too far and have replaced one problem with another.

Thanks. Sorry I meant fully close it to disable it completely.

 

[John.g]

No. Don't "fully open" it. It should be set to operate at the highest pressure difference that allows it to achieve its intended purpose.

If you are determined to play around open it by small amounts, say quarter turns until it reduces the 1840 noise. But, if you open it enough to completely eliminate the 1840 noise you'll probably have gone too far and have replaced one problem with another.

Fully opening it was simply to establish if it was/is plumbed in properly.

 

[John.g]

I have tried opening the lock shield valve a bit and closing it but made no difference whilst the noise was happening. The pump is built in to the boiler and it can run on either 70 percent or 100 percent. It’s on the default of 70 percent.

Any idea what make/model of circ pump fitted.?

 

[Tigermad]

Any idea what make/model of circ pump fitted.?

Hi. It’s inside an Ideal Vogue S32 gen boiler.

 

[John.g]

Hi. It’s inside an Ideal Vogue S32 gen boiler.

Thanks, could you post the setting up instructions of your ABV, it should then be relatively easy to set it up properly.

 

[Tigermad]

Thanks, could you post the setting up instructions of your ABV, it should then be relatively easy to set it up properly.

Here you go. Thanks

 

[John.g]

Here you go. Thanks
View attachment 36907 View attachment 36908

Straightforward enough.
1. Shut off the ABV, turn the setting knob clockwise to o.5
2. Ensure all zones (if fitted) on, and all TRV.s fully open.
3. Turn any/all room stats to max. (my suggestion)
4. Ensure boiler is actually firing or cycling on/off.
5. Very slowly turn ABV setting knob anticlockwise until the outlet pipe starts getting warm/hot.
6. Turn ABV setting knob clockwise by 1/2 a turn.
Forget the rest of the instructions for awhile and you can revisit them later.
Re 5 above. IMO, you can expect the pipe(s) to start to get warm at ~ setting 0.3 to 0.2.

 

[doitmyself]

the abv is before the zone valve from the boiler but after the zone valve coming down from the cylinder.

The ABV must be fitted between the flow and the pipe between zone valve and boiler. If it's on the wrong side of the valve there will be no flow to the boiler when the valve is closed, which defeats the purpose of the ABV.

 

[Tigermad]

The ABV must be fitted between the flow and the pipe between zone valve and boiler. If it's on the wrong side of the valve there will be no flow to the boiler when the valve is closed, which defeats the purpose of the ABV.

Hi. Thanks for the reply. Did you see my pic and post number 3? Does the position looks wrong ?

 

[Tigermad]

The first vertical pipe is the return. This has the zone valve attached. The furthest right says flow from boiler on it. The abv is on a pipe from the return to the flow. I am not sure what the other horizontal pipe is below the horizontal one with the abv. This joins to the flow but has its own pipe going to the boiler on the other end.

 

[John.g]

The first vertical pipe is the return. This has the zone valve attached. The furthest right says flow from boiler on it. The abv is on a pipe from the return to the flow. I am not sure what the other horizontal pipe is below the horizontal one with the abv. This joins to the flow but has its own pipe going to the boiler on the other end.

View attachment 36925
View attachment 36926

I thought it was thrashed out re the ABV positioning and the consensus was that it is installed correctly, my only slight unease concerns the vertical "return" pipe, this has a motorized valve attached which I would have thought is a bit unusual as they are normally installed on the flow.
I will just repeat what I said in some other post above, with the boiler firing normally and up to temperature, open (anticlockwise) the ABV fully to index 0.1, if the pipes on both sides of this don't get "red" hot in less than say 1 to 2 minutes then you have a problem. Just re close (clockwise) the ABV fully to index 0.5 after the test.

 

[doitmyself]

Hi. Thanks for the reply. Did you see my pic and post number 3? Does the position looks wrong ?

If pipe A in the pic below goes to the boiler, it's piped wrongly. But if pipe B goes to the boiler, it's correct.

 

[John.g]

If pipe A in the pic below goes to the boiler, it's piped wrongly. But if pipe B goes to the boiler, it's correct.

View attachment 36944

Correct, and of course also assumes that B is on the boiler flow, that test above should prove it one way or the other but surely it should be also possible to trace those lines, if not already done so.

 

[Tigermad]

Hi. Pipe a and b are the same pipe. If you mean directions then a goes into the loft to the unvented cylinder and b goes down towards the boiler. The whole pipe has return written on it.

 

[John.g]

Hi. Pipe a and b are the same pipe. If you mean directions then a goes into the loft to the unvented cylinder and b goes down towards the boiler. The whole pipe has return written on it.

Can you just do one thing please and post back, turn up the cylinder stat to max (normal setting should be 60C) and see which one of those pipes gets hot first.

 

[John.g]

Hi. Pipe a and b are the same pipe. If you mean directions then a goes into the loft to the unvented cylinder and b goes down towards the boiler. The whole pipe has return written on it.

Reading your reply again, literally, the (and as I suspected) zone valve if fitted on the SUPPLY or FLOW to the hot water cylinder coil, the RETURN is the vertical pipe so the ABV is the wrong way round?.

Here is your image with arrow.

 

[doitmyself]

Hi. Pipe a and b are the same pipe. If you mean directions then a goes into the loft to the unvented cylinder and b goes down towards the boiler. The whole pipe has return written on it.

A and B are actually two separate pipes which connect to the motorized valve; but that's not important. Your second sentence answers my question as pipe B goes to the boiler, so the bypass is installed correctly.

As for checking if the bypass is set correctly, yes, it's the short length of pipe between the bypass and pipe 'B' which you need to feel. However, if the motorized valve from the HW cylinder is closed so there is no flow coming through the MV from pipe A, then you can feel pipe B to check if the ABV is opening.

If pipe B is the HW return to the boiler, where does the heating return connect?

 

[JTplumbingservices]

If pipe A in the pic below goes to the boiler, it's piped wrongly. But if pipe B goes to the boiler, it's correct.

View attachment 36944

Where is the boiler and pump in relation to this pic?

 

[Tigermad]

Where is the boiler and pump in relation to this pic?

Hi. Sorry for the late replies I did not get notifications. The boiler is downstairs under the stairs directly below the airing cupboard. The pump is in the boiler I don't have one seperatesl as far as I know

 

[Tigermad]

A and B are actually two separate pipes which connect to the motorized valve; but that's not important. Your second sentence answers my question as pipe B goes to the boiler, so the bypass is installed correctly.

As for checking if the bypass is set correctly, yes, it's the short length of pipe between the bypass and pipe 'B' which you need to feel. However, if the motorized valve from the HW cylinder is closed so there is no flow coming through the MV from pipe A, then you can feel pipe B to check if the ABV is opening.

If pipe B is the HW return to the boiler, where does the heating return connect?

Not sure where the heating return connects sorry

 

[Tigermad]

Straightforward enough.
1. Shut off the ABV, turn the setting knob clockwise to o.5
2. Ensure all zones (if fitted) on, and all TRV.s fully open.
3. Turn any/all room stats to max. (my suggestion)
4. Ensure boiler is actually firing or cycling on/off.
5. Very slowly turn ABV setting knob anticlockwise until the outlet pipe starts getting warm/hot.
6. Turn ABV setting knob clockwise by 1/2 a turn.
Forget the rest of the instructions for awhile and you can revisit them later.
Re 5 above. IMO, you can expect the pipe(s) to start to get warm at ~ setting 0.3 to 0.2.

Hi. I've done your test and the pipe only stats to get very slightly warm at around 0.25. Even when fully open the pipe is only slightly warm is that correct? By slightly warm I mean nowhere as hot as the flow going into it.

 

[Tigermad]

I thought it was thrashed out re the ABV positioning and the consensus was that it is installed correctly, my only slight unease concerns the vertical "return" pipe, this has a motorized valve attached which I would have thought is a bit unusual as they are normally installed on the flow.
I will just repeat what I said in some other post above, with the boiler firing normally and up to temperature, open (anticlockwise) the ABV fully to index 0.1, if the pipes on both sides of this don't get "red" hot in less than say 1 to 2 minutes then you have a problem. Just re close (clockwise) the ABV fully to index 0.5 after the test.

Just tried this. The pipe on the return side doesnt get red hot just slightly hot when fully open. I have waited a good few minutes.

 

[John.g]

Not sure where the heating return connects sorry

Thanks, if the pipes on either side of the AAV are/were cold, the HW MV closed. With boiler on to CH, if you opened up the AAV fully do the pipes then get hot on both sides of it within a minute or less?. if they do then the AAV is operating/installed correctly, if they don't the there is something wrong.
I appreciate the question was asked a few times but not sure of your reply.

Edit: Just saw your other posts, thanks.

 

[Tigermad]

Thanks, if the pipes on either side of the AAV are/were cold, the HW MV closed. With boiler on to CH, if you opened up the AAV fully do the pipes then get hot on both sides of it within a minute or less?. if they do then the AAV is operating/installed correctly, if they don't the there is something wrong.
I appreciate the question was asked a few times but not sure of your reply.

Edit: Just saw your other posts, thanks.

Just done it. The small return pipe is only slightly warm. Nowhere near as hot as the flow pipe.

 

[John.g]

Just tried this. The pipe on the return side doesnt get red hot just slightly hot when fully open. I have waited a good few minutes.

There is definitely something amiss then, if the boiler and system contents are up to near normal running temperature of say 60 to 70C then both sides of the AAV should get equally very hot in a very short time when opened fully as you are effectively short circuiting the flow&return pipework.

 

[Tigermad]

There is definitely something amiss then, if the boiler and system contents are up to near normal running temperature of say 60 to 70C then both sides of the AAV should get equally very hot in a very short time when opened fully as you are effectively short circuiting the flow&return pipework.

The radiators had been fully on for only 10 mins. My boiler is set at 65. Maybe I didn't leave it long enough?

 

[John.g]

Perhaps, but you did say that the return is cool in comparison to the flow, try again after say 20 minutes, and let us know the result.

 

[Tigermad]

Perhaps, but you did say that the return is cool in comparison to the flow, try again after say 20 minutes, and let us know the result.

Thanks. So do I have to turn all rads fully on our can i just do it to 1 to make the boiler fire up and stay on? Bit of a pain having to keep going round them all

 

[Tigermad]

Hi. Another question. This isn't my cylinder but I have one of the little white cylinders too. But mine is at floor level. What is it?

 

[John.g]

Just 1 will do, just make sure the boiler is firing, thats all, or if you go to the boiler now and feel the Flow (top) pipe it should be quite hot, once it is just open up the AAV and both sides of it should get very hot as well in a very short time.

The "white cylinder" is a expansion vessel.

 

[Tigermad]

Just 1 will do, just make sure the boiler is firing, thats all, or if you go to the boiler now and feel the Flow (top) pipe it should be quite hot, once it is just open up the AAV and both sides of it should get very hot as well in a very short time.

The "white cylinder" is a expansion vessel.

Thanks. Just ran it with 1 on for literally a few seconds and it got red hot straight away. Wonder why it didn't do that earlier.