central heating flush issue

[coolideas]

I have been called in to sort a friend's heating system. They were constantly bleeding some of the radiators! The plumbing is a bit of a nightmare, done by the owner but cut and changed over the years. Originally there was a backboiler heating the system, this was removed and an oil boiler added outside. I moved the tank in the loft to a higher position, didn't seem to make it better. I decided to flush the system with a desludger. I opened the drain at the boiler and got about 30seconds of black then clear water! Then nothing. So I opened the cold supply to boiler from rads, an initial flow for 30secs then nothing! What can I do now?

 

[SJB060685]

Everytime air is sucked into the system black iron oxide (sludge) will form, as I'm sure you're aware of. From what you've said I'd say the system needs a proper power flush. Also what is the orientation of Vent, cold fill and pump?

 

[coolideas]

Everytime air is sucked into the system black iron oxide (sludge) will form, as I'm sure you're aware of. From what you've said I'd say the system needs a proper power flush. Also what is the orientation of Vent, cold fill and pump?

Thanks for the reply. I have bought a sludge clear additive to go in the system as I'm sure that is an issue. I first wanted to flush the system through with clean water before running it with the additive, but with no water coming out the pipes, there is obviously an air lock or sludge lock! Can I rig up a circulating pump (so no pressure just flow) and pump clean water from the boiler hot pipe to flush out through boiler return? Should the F&E tank be 3/4" pipe to system?
Thanks
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Also what is the orientation of Vent, cold fill and pump?
I noticed the owner had replaced an AAV on the cylinder coil outlet with a vent pipe to F&E tank, so there was no vent pipe originally. The F&E tank in loft only has a 1/2" pipe going into a 3)4" pipe which feeds a pipe to the boiler. The circulation pump is sitting vertically next to the old fireplace on the boiler supply, but there is a 't' off before it to a plastic 1/2" pipe (?).

 

[SJB060685]

This sounds I right mess and I'm struggling to picture it. When I say orientation I mean where are these pipes connecting into the system. It should be vent then cold fill (150mm apart) and then pump, this provides a positive pressure throughout the system. 15mm feed and expansion pipe is fine for boilers up to 25KW so my OFTEC book says, obviously tank capacity is determined by system volume. If you could supply a drawing of system layout and vent and cold fill entry point I could picture it better.
Rigging up your own system to try and remove blockages will be a pain. You can hire the machines on a daily rate which will do the job properly. We only ever hired the machine as we didn't do too much of it to warrant purchasing one.
What is that plastic pipe feeding by pump as well and how close to boiler?

 

[coolideas]

Ok I spent 4 hours trying to work out the system today and flush. I managed to rig up a supply from the mains and flush through from the boiler pipes, plenty black coming out! There is no knowing how far round the system this went though, it may have just gone through the cylinder coil and back. What I did discover was that the kitchen tap dripped when i flushed the heating system, bare in mind that the kitchen tap is not connected to this system!!! but a separate heating system for the extension of the house.
After firing up the boiler again all three rads downstairs got roasting but nothing upstairs. I could hear the pump alternating in pitch and figured the pump was not pumping effectively especially as the pipe above the rad take off (going to cylinder coil) did not get hot!
See diagram for the best I can figure out without ripping up floorboards etc.

Cheers
Dave

 

[SJB060685]

I've had a look at diagram, well done. From that it looks as though the pump is pumping straight over through vent, each time this happens air will be sucked in causing sludge to accumulate. I must add when flushing an open vented system the cold feed and vent should be blanked off. You say the pump was making an unnatural sound, a pump when spinning acts as a magnet, drawing in and accumulating the magnetic sludge, I suspect this is clogged up, working enough to pump over through a path of minimal resistance but not enough to get heat to up stairs rads which could offer a lot of resistance or further blockages. Sludge to start off with will gather at bottom of rads, further building up over time. You could stick a strong magnet against the flow and return of upstairs rads to see if there is sludge there, remember copper cant be magnetized but steel obviously is, so put magnet against copper pipes, if it sticks you know theres a large build up of sludge. I once had a system with 22mm pipe having an internal bore of 2 or 3mm the sludge was that bad, piped similar to this picture.
Personally I would recommend the whole system be reconfigured to prevent this venting over and properly power flushed. Sealed system will do away with the worry of venting over and allow positioning of the pump where it is, it needs to be fully pumped, complete thermostatic control with independent zones. As it stands, from what your diagram says matters wont improve

 

[coolideas]

Thanks for your reply. Unfortunately the guy has chopped and changed stuff over the years it is very difficult to know where some of the pipes are, like water coming out of kitchen sink tap in earlier post. Why is there a 1/2" pipe T'd off from below pump to just before cylinder? Looking at it again I might have it wrong, it may go into the return from cylinder coil, sorry.
I removed the pump, no sludge inside. I had to remove a length of pipe with pump attached as the pump valves were so rusted up to pump body I couldn't get the free. Will try some heat on them tomorrow.
Found some interesting 'faults' as I was inspecting the system. The drain at boiler was not tightened up, one bleed valve was loose on a radiator (rust line down side suggested its been going for a while!), a valve on the fill line was closed!
I don't really want to change it to sealed system due to not knowing the full system layout under the concrete floors etc. Whats the best thing to change this layout for the better?

Many thanks
Dave

 

[SJB060685]

With a drain off open, or not completely closed and a bleed valve the same you'll be drawing air, all that mounts up. I cant say why the tap is dripping because I genuinely don't know. You need to change the pipework so it's not venting over and have independent zones with full thermostatic control

 

[coolideas]

Ok so if I move the expansion pipe to exit from the bottom of hot water from boiler before the pump, I can use the 1/2" that is already there and connect to 1/2" coming off the intake to coil in cylinder. Then put an AAV there instead?

 

[SJB060685]

You need to re pipe vent position to come off before the pump, as it is its pumping straight over and drawing in air, power flush or any flush is pointless until that is changed. Zone valves and thermostats should be installed as well.

 

[John.g]

Ok so if I move the expansion pipe to exit from the bottom of hot water from boiler before the pump, I can use the 1/2" that is already there and connect to 1/2" coming off the intake to coil in cylinder. Then put an AAV there instead?

The "normal" method now I think is to have the pump on the boiler Flow side and from the boiler and as post #5 stated It should be vent then cold fill (150mm apart) and then pump, don't know if this will work as well where the pump is installed on the boiler return but if its been done this way before then? although I would think that the vent woks best on the hot, flow side.
I know you don't like the idea of a sealed system but there are lots of houses around me that were converted from oil to gas and Bord Gais installed all of them as "semi-sealed", a lot more forgiving than a fully sealed system. All you need to do is install a swing check NRV on a horizontal piece of the cold feed, install a E.vessel preferably as close to the pump suction as possible, and pre pressurise it to 0.3 bar, assuming a 12 litre E.vessel and volume contents of even 100 litres then the max pressure with everything heated up will not exceed 0.75bar to 0.9 bar which any system should have no problem with as the gravity head in a vented systen is ~ 0.3/0.4 bar anyway.

You could also consider a combined vent and cold feed (like mine, from new) but you would need to install a 3/4 ins vent for this.

 

[SJB060685]

I've never seen a semi sealed system so cant comment. I have known systems with a combined vent and cold fill and I believe would stop venting over if installed after pump. If you opt for this route then the boiler must have an overheat thermostat (which it will) but also must be boiler manufacturer approved, so my heating guide says. Perhaps moving the position of pump seeing as vent and feed are separate to the return and plumbed in correctly can eliminate the venting over.
The vent should always be on the flow, unrestricted and sized correctly, if it were on the return you'd have nowhere for the heated water to escape in the event of a problem.
Having said all this the homeowner would massively benefit from an upgraded system with full thermostatic controlled zones.

 

[coolideas]

Sounds interesting. Things you need to understand, I'm on an offshore island so can't nip to the shop to get parts! I'm working on a mixture of metric and imperial pipework/fittings so it's never simple. The owner doesn't understand about plumbing but installed this system many years ago, then chopped and changed it as he thought fit! There are two systems in the house but are probably connected somehow, re the dripping tap in one side when flushing the heating on the other!
I love sealed systems but not knowing what the owner has done makes me reluctant to alter what's there. Today I removed a gate valve in the feed line that was locked closed. No simple job, I had to dismantle shelves and remove a support board to gain access. Also replaced the pump. Guests are coming next week so I will fire the system up so they have heat then alter after new year when I have all the fitting ready.
Thank you guys for your input, I have learnt something new so that is always good.
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You could also consider a combined vent and cold feed (like mine, from new) but you would need to install a 3/4 ins vent for this.

Never heard of semi sealed system.
Where is the combined vent/feed in your system? This one has 3/4" cold feed most of the way down to boiler so easy to change 1/2" from feed tank to just under loft floor to 3/4".
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You could also consider a combined vent and cold feed (like mine, from new) but you would need to install a 3/4 ins vent for this.

Never heard of semi sealed system.
Where is the combined vent/feed in your system? This one has 3/4" cold feed most of the way down to boiler so easy to change 1/2" from feed tank to just under loft floor to 3/4".
[automerge]1576968753[/automerge]

You could also consider a combined vent and cold feed (like mine, from new) but you would need to install a 3/4 ins vent for this.

Never heard of semi sealed system.
Where is the combined vent/feed in your system? This one has 3/4" cold feed most of the way down to boiler so easy to change 1/2" from feed tank to just under loft floor to 3/4".

 

[SJB060685]

When you say there are two systems do you mean two heating systems? You keep mentioning the dripping tap when flushing, is this tap tank fed or off the mains?

 

[John.g]

Sounds interesting. Things you need to understand, I'm on an offshore island so can't nip to the shop to get parts! I'm working on a mixture of metric and imperial pipework/fittings so it's never simple. The owner doesn't understand about plumbing but installed this system many years ago, then chopped and changed it as he thought fit! There are two systems in the house but are probably connected somehow, re the dripping tap in one side when flushing the heating on the other!
I love sealed systems but not knowing what the owner has done makes me reluctant to alter what's there. Today I removed a gate valve in the feed line that was locked closed. No simple job, I had to dismantle shelves and remove a support board to gain access. Also replaced the pump. Guests are coming next week so I will fire the system up so they have heat then alter after new year when I have all the fitting ready.
Thank you guys for your input, I have learnt something new so that is always good.
[automerge]1576968752[/automerge]

Never heard of semi sealed system.
Where is the combined vent/feed in your system? This one has 3/4" cold feed most of the way down to boiler so easy to change 1/2" from feed tank to just under loft floor to 3/4".
[automerge]1576968752[/automerge]

Never heard of semi sealed system.
Where is the combined vent/feed in your system? This one has 3/4" cold feed most of the way down to boiler so easy to change 1/2" from feed tank to just under loft floor to 3/4".
[automerge]1576968753[/automerge]

Never heard of semi sealed system.
Where is the combined vent/feed in your system? This one has 3/4" cold feed most of the way down to boiler so easy to change 1/2" from feed tank to just under loft floor to 3/4".

The vent should be 3/4 ins, the cold feed can remain 1/2 ins, just cut it and bring it around under the Feed&Expansion tank and then T it into the (now) 3/4 ins vent, then blank off the now defunct 1/2 ins cold feed as low down as possible.
My system just has the cold feed teed into the Vent where it passes up very close to the Feed&Expansion Tank, the system is very very clean after over 40 years with the very occasional drop of inhibitor added now and then with still some of its original rads.

 

[coolideas]

When you say there are two systems do you mean two heating systems? You keep mentioning the dripping tap when flushing, is this tap tank fed or off the mains?

Yes the house extension has a heat pump and solar for hot water. I recently changed the hot water tank as the owner didn't know about the anode in the tank so it was never replaced and hence the fittings started to corrode. There were two heating coils to the cylinder one for solar and one the other heat source which I assumed was the old back boiler(now oil boiler). It was only when I asked where was the drain for that, that the owner remembered he has the heat pump system! That's what I'm up against
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The vent should be 3/4 ins, the cold feed can remain 1/2 ins, just cut it and bring it around under the Feed&Expansion tank and then T it into the (now) 3/4 ins vent, then blank off the now defunct 1/2 ins cold feed as low down as possible.
My system just has the cold feed teed into the Vent where it passes up very close to the Feed&Expansion Tank, the system is very very clean after over 40 years with the very occasional drop of inhibitor added now and then with still some of its original rads.

Not so easy on mthis system. If you check my diagram the vent pipe is only 1/2" and in the wrong place! This system originally didn't have a vent pipe. The feed pipe though goes down to boiler before pump, starts as 1/2" in loft then into 3/4" from loft floor. So I was thinking, extend the 3/4" up and over F&E tank and t ,1/2" feed into that?

 

[SJB060685]

This just gets better and better . Was the cylinder you replaced copper or steel? So the new cylinder has two coils, one fed by heat pump and the other solar? So what does the oil boiler do? Just heating?

 

[coolideas]

This just gets better and better . Was the cylinder you replaced copper or steel? So the new cylinder has two coils, one fed by heat pump and the other solar? So what does the oil boiler do? Just heating?

The solar and heat pump are on the 'separate' extension system, nothing to do with the oil boiler. The oil boiler heats water and central heating in the main house with a copper cylinder.
The tank I replaced in the extension was a steel tank, now it has a stainless.
I have seen pipes here held together with jubelee clips . Many are heated then pushed over the other pipe to join, like I said it's an offshore island, only 3mile x 1mile 80 residents, so folk make the best they can at the time but then never go back and do the job properly when they have the fittings.

 

[SJB060685]

Here's a picture from my heating guide to help you visualise it. On the right is your typical close coupled vent and feed, this orientation provides a positive pressure throughout the system, preventing air be drawn in from leaky valves etc a d obviously preventing pumping over, this is desired layout.
On the left is a layout you could achieve by repositioning pump and cold fill. The neutral point will be where the feed enters and a positive pressure between pump and that, the rest of system will be under negative pressure and should prevent the pumping over, although will draw air in if you have leaky valves like glands on rad valves etc.
Vent should always be a minimum off 22mm, no exceptions.
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Stainless steel is not susceptible to corrosion like other cylinders so that was a good choice. Have a look at image above and see what you think mate.

 

[John.g]

Yes the house extension has a heat pump and solar for hot water. I recently changed the hot water tank as the owner didn't know about the anode in the tank so it was never replaced and hence the fittings started to corrode. There were two heating coils to the cylinder one for solar and one the other heat source which I assumed was the old back boiler(now oil boiler). It was only when I asked where was the drain for that, that the owner remembered he has the heat pump system! That's what I'm up against
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Not so easy on mthis system. If you check my diagram the vent pipe is only 1/2" and in the wrong place! This system originally didn't have a vent pipe. The feed pipe though goes down to boiler before pump, starts as 1/2" in loft then into 3/4" from loft floor. So I was thinking, extend the 3/4" up and over F&E tank and t ,1/2" feed into that?

My vent is practically in the same position, ie, its a "continuation" of the HW cylinder coil entry and the cold water fill is just teed into this, yours seems to be in the correct position but obviously wrong at 1/2". You can't or shouldn't use the cold feed as a vent because its on the boiler return.

Your pump is on the boiler flow. IMO, the easiest/best chance of success is to connect a 1 litre E.vessel here just before the pump (its just one T) pre pressurised to 0.3 bar, install a swing check valve in the cold feed and blank off the 1/2" vent where it comes off the HW cylinder coil entry. All the other systems may work, close coupled etc can work but some of these vented systems can and do still give problems with air ingress etc.

 

[SJB060685]

You're proposing a semi sealed system correct? If he chooses this route he would still need to install a PRV and the volume of expansion vessel needs to be sized correctly, determined by system volume a d pressure, I can work out the volume of vessel needed if you supply me with this.

 

[John.g]

Yes, of course, I assumed that the boiler had a PRV fitted, but this should be checked out first, I have no idea of the system volume but doubt it would be more than 100 litres, so based on this and 0.3 bar pre pressure and a mean boiler flow/return temp of 70C then my calculations give a final pressure of < 1.0 bar ( 0.66 bar) with a 12 litre E.vessel.

 

[SJB060685]

My calculations suggest with a system volume of 100 litres and a vessel charge of one bar then a 10.9 litre vessel will be sufficient at normal operating temperatures, obviously waters thermal expansion coefficient changes at higher temperatures but that's irrelevant as your system wont. A 12 litre would be fine, a oversized vessel is not a problem but too small or under charged is.

 

[John.g]

Yes the house extension has a heat pump and solar for hot water. I recently changed the hot water tank as the owner didn't know about the anode in the tank so it was never replaced and hence the fittings started to corrode. There were two heating coils to the cylinder one for solar and one the other heat source which I assumed was the old back boiler(now oil boiler). It was only when I asked where was the drain for that, that the owner remembered he has the heat pump system! That's what I'm up against
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Not so easy on mthis system. If you check my diagram the vent pipe is only 1/2" and in the wrong place! This system originally didn't have a vent pipe. The feed pipe though goes down to boiler before pump, starts as 1/2" in loft then into 3/4" from loft floor. So I was thinking, extend the 3/4" up and over F&E tank and t ,1/2" feed into that?

Just reading your post there again, maybe you are suggesting moving the cold feed from its existing location to just before the pump (to act as the vent) and then "extend the 3/4" up and over F&E tank and t ,1/2" feed into that". then yes that may work as a combined cold feed and vent.

 

[coolideas]

Got the system up and running all radiators hot, BUT, the pipe that was market with red tape at the boiler turns out to be the cold return! Surely that means the pump was pumping the wrong way round the system?! Also after everything got hot the expansion pipe from the top of the cylinder started dripping! I hate this guy's setup. I'm leaving it as is for now until after new year.

 

[SJB060685]

If it was pumping back through boiler flow that is dangerous as theres nowhere for the super heated water to escape up through vent, it would also explain the air being sucked in that way. If the hot water cylinder is venting over then that suggests the water is too hot, again dangerous as this could build up and eventually cause header tank to collapse releasing many litres of scolding hot water down through the ceiling.
This happen in my town a few years ago, although due to a faulty immersion heater but the end result was a toddler was killed in their sleep.
The more you find and say the worse this sounds.
Honestly I'm at the point now where all I will suggest is isolate system and fully upgrade after Christmas, it will be a nice job for you, a good little earner but this sounds incredibly dangerous and what you have to remember is you're the last guy to touch it, effectively making you responsible and liable. Personally I would walk away from this, it's not worth the hassle.

 

[John.g]

So the right hand (red) pipe actually goes into the bottom of the boiler and the left hand (blue) comes off the top of the boiler?? and the pump is on this (red) return pumping Upwards?.

 

[coolideas]

So the right hand (red) pipe actually goes into the bottom of the boiler and the left hand (blue) comes off the top of the boiler?? and the pump is on this (red) return pumping Upwards?.

The boiler has two pipes(obviously) coming from the top so I have no idea which is which! I went by the red tape that was on one of the pipes, but when I re-established the flow from F/E tank the water came out of the pipe marked red, which I had disconnected to .
Unfortunately the guy who installed the boiler is not a plumber and he was the last guy to try and fix the non working issue but obviously missed all the issues I found. He has said he doesn't want to do any more work on the system, I'm no

If it was pumping back through boiler flow that is dangerous as theres nowhere for the super heated water to escape up through vent, it would also explain the air being sucked in that way. If the hot water cylinder is venting over then that suggests the water is too hot, again dangerous as this could build up and eventually cause header tank to collapse releasing many litres of scolding hot water down through the ceiling.
This happen in my town a few years ago, although due to a faulty immersion heater but the end result was a toddler was killed in their sleep.
The more you find and say the worse this sounds.
Honestly I'm at the point now where all I will suggest is isolate system and fully upgrade after Christmas, it will be a nice job for you, a good little earner but this sounds incredibly dangerous and what you have to remember is you're the last guy to touch it, effectively making you responsible and liable. Personally I would walk away from this, it's not worth the hassle.

Thankfully they don't use this side of the house, it's rented in the summer and a teacher in one room for the school term. So heating is off now. I'm pretty sick of it myself, every day something new turns up!
I'll do more investigating this week to try and clarify which pipe is which etc.

 

[John.g]

Its amazing what "systems" are out there. a few years ago a neighbour of mine mentioned in passing that he would find the hi limit stat (Firebird oil boiler) tripped out on some mornings, he had had the circ pump changed out about 4 years previously. I eventually had a look and found that the replacement pump which replaced the original one also installed in the flow was pumping downwards through the boiler so the boiler stat was actually measuring the return temp and consequently the flow temperature (going back through the return) was 10/15C higher than the set point, it was only when the boiler was off overnight that the very hot water was rising up through the boiler and tripping the hi limit stat, I just reversed the pump and all was well. This boiler, like mine has a 3 bar PRV fitted on top of the boiler. BUT if I didn't have the time there and then to reverse the pump, I would have insisted that the system was shut down and remained so until rectified.

 

[SJB060685]

There you go John, a classic example

 

[coolideas]

Its amazing what "systems" are out there. a few years ago a neighbour of mine mentioned in passing that he would find the hi limit stat (Firebird oil boiler) tripped out on some mornings, he had had the circ pump changed out about 4 years previously. I eventually had a look and found that the replacement pump which replaced the original one also installed in the flow was pumping downwards through the boiler so the boiler stat was actually measuring the return temp and consequently the flow temperature (going back through the return) was 10/15C higher than the set point, it was only when the boiler was off overnight that the very hot water was rising up through the boiler and tripping the hi limit stat, I just reversed the pump and all was well. This boiler, like mine has a 3 bar PRV fitted on top of the boiler. BUT if I didn't have the time there and then to reverse the pump, I would have insisted that the system was shut down and remained so until rectified.

Systems over here are appalling, I have had to sort out two wrongly plumbed systems here this year, this is the third.
The last one, had a new bathroom installed with a raised floor, the floor rotted after a year so I was called in to redo it. The water came through 1/2" pipe from a tank with about 6" head into a shower pump (3/4") inlet and two sinks, two toilets and the shower! Pump was sitting on the hardboard ceiling of one of the toilets, loud every time it came on.
In that house they had disconnected the supply to the F/E tank as it had cracked, the owner was taking 5lit containers into the loft to fill it! Honestly you wouldn't believe the stuff that goes on.