Banging pipes on solid fuel stove system

esquilax

I posted a while back about an issue with the copper cylinder in our CH/HW system that frequently springs leaks. As promised here is some detail about the other issue we have with it: banging pipes.

There are two heat sources, a solid fuel stove and an oil-fired boiler. There is an indirect cylinder with a single coil and seven radiators. Here is a photo of the cupboards in our kitchen containing the cylinder and most of the other pipework. I've drawn the path of some of the pipework that has been obscured to hopefully make it clearer. Going out through that hole in the wall are the pipes to the stove.

Obscured in the photo by the door frame to the left of the cylinder is a loop off the flow and return that connects to two upstairs radiators, the most effective in the house. Also, you can see a white pipe thermostat on the flow pipe of the cylinder. This cuts in at about 60 degrees and turns on the radiator circulating pump (at floor level, not visible). I think the installer came back and put this on after we first told him about the banging pipes issue (>20 years ago now)

The most notable thing about our system for me is the complete lack of any valves, electrically actuated or otherwise. The system does actually work quite well despite this - the boiler circuit and radiator circuits don't get hot from the heat of the stove without their respective circulating pumps being on.

The issue is that if the pipe stat is set low enough that the pipes don't bang, it means the circulating pump is on a lot and the cylinder doesn't get as hot as it should.

After lighting a big fire and setting the stat so it wouldn't cut in, I traced the source of the banging noise to the tees where the stove piping meets the boiler and cylinder piping. The rest of the noise is mostly the system resonating from this point. I recorded it and could post it, just in case there's anyone who can diagnose plumbing problems by their distinctive sound.

While feeling the pipes around the the tees, I noticed the flow of water in the pipes seems to be very turbulent. Not only can you hear bangs, but very loud gushing sounds. There are distinct hot and cold patches on the pipes - The flow pipe of the coil might be boiling hot while the return is not hot at all. Then you'll hear a couple of bangs, the sound of water rushing past and suddenly it's too hot to touch at all.

The overall rise from the stove to the cylinder is less than one meter and as you can see the pipework contains right angle joints and horizontal sections rather than a clear rise. Personally I think this is the culprit and I was thinking of relocating the cylinder (not the one you see in the photo, but perhaps a new stainless steel one) to an upstairs location.

1) Is there a diagram, anywhere, for how a solid fuel + boiler system should be piped? I certainly can't find one. Plenty of people saying "don't do it" and not really explaining why, but nobody saying how you should do it.
2) Am I correct in saying that regulations dictate that I couldn't put a mid-position valve on the stove loop, directing the heated water to either the cylinder (and "safety" radiators) or the main radiator loop? The objective would be to allow the radiators to be heated from the stove while preserving the heat of the water in the cylinder. This valve could then be controlled by the pipe thermostat. I'm fairly sure it isn't allowed but I'm struggling to understand why when there is no failure mode of such a valve that results in the heated water having nowhere to go.
3) Any thoughts on my theory of where the noise is coming from? Would you expect locating the cylinder higher up to help?

Thanks everyone for reading my long post.

ART6

esquilax wrote: »

I posted a while back about an issue with the copper cylinder in our CH/HW system that frequently springs leaks. As promised here is some detail about the other issue we have with it: banging pipes.

There are two heat sources, a solid fuel stove and an oil-fired boiler. There is an indirect cylinder with a single coil and seven radiators. Here is a photo of the cupboards in our kitchen containing the cylinder and most of the other pipework. I've drawn the path of some of the pipework that has been obscured to hopefully make it clearer. Going out through that hole in the wall are the pipes to the stove.

Obscured in the photo by the door frame to the left of the cylinder is a loop off the flow and return that connects to two upstairs radiators, the most effective in the house. Also, you can see a white pipe thermostat on the flow pipe of the cylinder. This cuts in at about 60 degrees and turns on the radiator circulating pump (at floor level, not visible). I think the installer came back and put this on after we first told him about the banging pipes issue (>20 years ago now)

The most notable thing about our system for me is the complete lack of any valves, electrically actuated or otherwise. The system does actually work quite well despite this - the boiler circuit and radiator circuits don't get hot from the heat of the stove without their respective circulating pumps being on.

The issue is that if the pipe stat is set low enough that the pipes don't bang, it means the circulating pump is on a lot and the cylinder doesn't get as hot as it should.

After lighting a big fire and setting the stat so it wouldn't cut in, I traced the source of the banging noise to the tees where the stove piping meets the boiler and cylinder piping. The rest of the noise is mostly the system resonating from this point. I recorded it and could post it, just in case there's anyone who can diagnose plumbing problems by their distinctive sound.

While feeling the pipes around the the tees, I noticed the flow of water in the pipes seems to be very turbulent. Not only can you hear bangs, but very loud gushing sounds. There are distinct hot and cold patches on the pipes - The flow pipe of the coil might be boiling hot while the return is not hot at all. Then you'll hear a couple of bangs, the sound of water rushing past and suddenly it's too hot to touch at all.

The overall rise from the stove to the cylinder is less than one meter and as you can see the pipework contains right angle joints and horizontal sections rather than a clear rise. Personally I think this is the culprit and I was thinking of relocating the cylinder (not the one you see in the photo, but perhaps a new stainless steel one) to an upstairs location.

1) Is there a diagram, anywhere, for how a solid fuel + boiler system should be piped? I certainly can't find one. Plenty of people saying "don't do it" and not really explaining why, but nobody saying how you should do it.
2) Am I correct in saying that regulations dictate that I couldn't put a mid-position valve on the stove loop, directing the heated water to either the cylinder (and "safety" radiators) or the main radiator loop? The objective would be to allow the radiators to be heated from the stove while preserving the heat of the water in the cylinder. This valve could then be controlled by the pipe thermostat. I'm fairly sure it isn't allowed but I'm struggling to understand why when there is no failure mode of such a valve that results in the heated water having nowhere to go.
3) Any thoughts on my theory of where the noise is coming from? Would you expect locating the cylinder higher up to help?

Thanks everyone for reading my long post.

From your description I would suspect you are experiencing steam hammer (a variant of water hammer but basically the same thing). What can happen is that the water from the stove is getting too hot as the circulation is insufficient. As a result, anywhere there is a pressure drop the water starts to flash off into steam which, when it arrives at a slightly cooler area, immediately recondenses and the water fills the void with a loud bang. That implies that somewhere in the flow from the stove there is a restriction -- even too many badly fitted tees can do it. So if that is the case you need to increase the circulation from the stove.

I assume it has its own circulating pump, and that should be on maximum setting. You should also check that the stove has its own independant vent pipe to the attic header tank. If all of that is correctly installed and if the circulating pump is running properly then I suspect your only solution would be to increase the size of the stove pipework and run it better.

The banging and rushing sounds, together with the wild fluctuations in temperature certainly wouldn't do the cylinder any favours since the shock waves would be transmitted through the cylinder contents to its wall and seams. The cylinder metal thickness is a lot less than that of the pipes, and the seams are the weak points. Excessive temperature fluctuations can also cause stress corrosion.

Having a solid fuel stove and an oil fired boiler on an atmostpheric system is common -- I have one that works without any problems and has done so for 35 years. On my system both boilers have their own circulating pumps, and there is a thermostat on the solid fuel boiler pipework that turns its circulating pump on and off. That has an isolating switch that enables the stat when we light a fire, but then we have to remember to turn off the oil boiler because they won't both work together -- too much flow (possibly that is part of your problem -- both on at the same time?). I could have fitted electrics to turn off the oil boiler automatically and a second stat to register when a fire is lit in the stove, but I have never bothered.

On the coil connections to the cylinder there would normally be a balancing valve on the return line and a bypass between the flow and return. That would then allow you to apportion flow between the coil and the radiators, but you would need to sort the overheating problem first or fitting such valves would make it worse.

I wouldn't think that relocating the cylinder would help, and it might even make things worse.

The reason suspect the causes I have described is that I have come across similar situations in industrial systems, and because on my system at home if we light the stove but forget to switch on the stat we soon enough get rumbling sounds as the stove starts to boil. If we then turn on the stat there is a minute or two of quite loud bangs and hisses until the system stabilises, and it would be possible to fry rashers on the radiators:p

esquilax

ART6 wrote: »

From your description I would suspect you are experiencing steam hammer (a variant of water hammer but basically the same thing). What can happen is that the water from the stove is getting too hot as the circulation is insufficient. As a result, anywhere there is a pressure drop the water starts to flash off into steam which, when it arrives at a slightly cooler area, immediately recondenses and the water fills the void with a loud bang. That implies that somewhere in the flow from the stove there is a restriction -- even too many badly fitted tees can do it. So if that is the case you need to increase the circulation from the stove.

By badly fitted, I presume you mean that there's just too many of them too close together and the installer should have anticipated the effect it'd have - i.e. there wouldn't be anything to be gained from redoing them in the same positions.

ART6 wrote: »

I assume it has its own circulating pump, and that should be on maximum setting. You should also check that the stove has its own independant vent pipe to the attic header tank. If all of that is correctly installed and if the circulating pump is running properly then I suspect your only solution would be to increase the size of the stove pipework and run it better.

It does not have its own circulating pump. The oil boiler has its own, but the circulating pump for the solid fuel is located out on the radiator loop.

Given that the water is obviously not circulating properly, putting one near the stove was one of the first potential solutions that came to mind but I thought that the loop between the solid fuel stove and the cylinder must not have any valve or pump installed in it - that it must do its work by gravity alone. This is where I came up with the idea of moving it.

If I can safely have a pump near the stove then that's what I'm inclined to do. If it resolves the banging problem (and I'd be surprised if it doesn't) then I will look into the issue of valves. I just learnt of the existence of something called an "injector tee" which it sounds like he should have installed too but probably not worth worrying about now.

ART6 wrote: »

The banging and rushing sounds, together with the wild fluctuations in temperature certainly wouldn't do the cylinder any favours since the shock waves would be transmitted through the cylinder contents to its wall and seams. The cylinder metal thickness is a lot less than that of the pipes, and the seams are the weak points. Excessive temperature fluctuations can also cause stress corrosion.

Well I'd be delighted if it turned out to fix that too, although for the sake of some extra space in the kitchen I would still like to move it upstairs in the longer term.

ART6 wrote: »

Having a solid fuel stove and an oil fired boiler on an atmostpheric system is common -- I have one that works without any problems and has done so for 35 years. On my system both boilers have their own circulating pumps, and there is a thermostat on the solid fuel boiler pipework that turns its circulating pump on and off. That has an isolating switch that enables the stat when we light a fire, but then we have to remember to turn off the oil boiler because they won't both work together -- too much flow (possibly that is part of your problem -- both on at the same time?). I could have fitted electrics to turn off the oil boiler automatically and a second stat to register when a fire is lit in the stove, but I have never bothered.

We actually don't have an issue with our system once there is a circulating pump running, not even if the stove and boiler are both lit. From your stove do you have two separate connections for central heating and hot water? Most diagrams seem to show it done this way and our new stove has two sets of tappings but we're only using one of them.

ART6 wrote: »

On the coil connections to the cylinder there would normally be a balancing valve on the return line

Could you explain more about this? We don't have one anyway.

ART6 wrote: »

and a bypass between the flow and return. That would then allow you to apportion flow between the coil and the radiators, but you would need to sort the overheating problem first or fitting such valves would make it worse.

I wouldn't think that relocating the cylinder would help, and it might even make things worse.

Ok, if I could get it working in the position it's currently in, then I'd feel more confident about moving it should I ever need to.

Thanks very much for the info.

ART6

esquilax wrote: »

By badly fitted, I presume you mean that there's just too many of them too close together and the installer should have anticipated the effect it'd have - i.e. there wouldn't be anything to be gained from redoing them in the same positions.

Going by your photo the installer didn't do a very tidy job at least. Redoing the tees wouldn't make any difference as you assume.

It does not have its own circulating pump. The oil boiler has its own, but the circulating pump for the solid fuel is located out on the radiator loop.

Therein lies the problem I would think. The system from the stove is relying on thermal lift alone and there isn't enough of it given the pipe layout and the position of the cylinder.

Given that the water is obviously not circulating properly, putting one near the stove was one of the first potential solutions that came to mind but I thought that the loop between the solid fuel stove and the cylinder must not have any valve or pump installed in it - that it must do its work by gravity alone. This is where I came up with the idea of moving it.

Provided that the stove has an independant cold water supply and an open vent to the attic tank you can fit a pump and, if you wish, valves. However, any valves must be electrical power to close types.

If I can safely have a pump near the stove then that's what I'm inclined to do. If it resolves the banging problem (and I'd be surprised if it doesn't) then I will look into the issue of valves. I just learnt of the existence of something called an "injector tee" which it sounds like he should have installed too but probably not worth worrying about now.

I would expect that if you fit a pump in the stove flow line you would overcome the problem alright. On your existing system, with a circulating pump on the oil boiler but none on the stove, then when the latter is unlit I would expect that the oil boiler would be circulating hot water through it and wasting a lot of heat.
Well I'd be delighted if it turned out to fix that too, although for the sake of some extra space in the kitchen I would still like to move it upstairs in the longer term.

In the absence of a circulating pump and relying on thermal lift (a quite normal arrangement) then I would agree that moving the cylinder upstairs would certainly help.

We actually don't have an issue with our system once there is a circulating pump running, not even if the stove and boiler are both lit. From your stove do you have two separate connections for central heating and hot water? Most diagrams seem to show it done this way and our new stove has two sets of tappings but we're only using one of them.

This paragraph pretty much confirms the diagnosis. The pipework layout and the height of the cylinder is not permitting sufficient thermal lift. The radiator pump is providing the circulation when it's on. On our system both the boiler and the stove have their own pumps, and both deliver to the cylinder coil with the radiator connections coming off the flow and return pipes. There is a coil bypass and a balance valve in the return line that allows me to reduce the flow through the coil so as to increase the flow through the radiators. The bypass is simply a valve and pipe connecting the coil flow and return outside the cylinder, so that when it's open the water does not flow through the coil. The balance valve is simply a globe valve in the coil return, so that closing it in and opening the bypass a little diverts some of the hot water away from the coil and towards the rads.

Central heating diagrams do usually show separate flow and return lines for the hot water and the radiators, relying on thermal lift for the cylinder circulation. That's OK in a house, but I have a bungalow with the cylinder some way away from the stove and very little higher, so an unpumped system wouldn't work.

Ok, if I could get it working in the position it's currently in, then I'd feel more confident about moving it should I ever need to.

If it was my system I'd be inclined to shift the radiator pump to the stove flow line and fit a bypass and balance valve to the cylinder. That way you would get circulation and radiators without the accoustics!