Water being PUMPED into CH Feed & Expansion Tank

[kildonan]

We have a problem of warm/hot water being PUMPED into the F&E tank via the expansion pipe. It doesn't happen all the time. Someone suggested that it could be caused by the pump being positioned in the wrong place in the system (but it seems correct) or by sludge build-up forcing water to flow up the expansion pipe.

The system was installed by an slightly eccentric plumber fifteen years ago. Instead of using a single pump and a motorized valve, he used two independently wired pumps, one on the return from the DHW cylinder and one on the return from the Rads circuit. He also connected the feed directly to the blanked off flow connection on the oil boiler. Another minor problem is that the rads upstairs get warm in the summer when the CH should be off and the DHW is on, persumably it is acting as a gravity system, because there is no valve to shut off the CH circuit.

The water jacket failed on the Potterton Statesman boiler and I'd like to sort out the problems in the system while I'm at it. I'm replacing the boiler myself, after I gave up waiting for our local plumber to turn up (twelve weeks so far).

The pumps are both positioned beside the boiler pumping return water into the boiler. The feed and expansion tank is twenty feet directly above the boiler. The flow and returns to and from DHW and CH Rads are all 22mm plastic, because the pipes were pulled up behind the lathe and plaster dry lining to keep it concealed and minimise making good.

Should I convert to a conventional system controlled by a motorised valve? Should I move the position of the pump? Should I think about upsizing the flow and return pipes (although the upheaval this would cause would be immense)? What's the best way to remove sludge from the system?

Thanks in anticipation

Chris M

 

[Softus]

We have a problem of warm/hot water being PUMPED into the F&E tank via the expansion pipe. It doesn't happen all the time. Someone suggested that it could be caused by the pump being positioned in the wrong place in the system (but it seems correct) or by sludge build-up forcing water to flow up the expansion pipe.

Do you mean that it's pumped out (a) via the cold feed from the F&E cistern, or (b) via the vent?

And do you have separate cold feed and vent pipes, or combined?

If separate, where does the vent pipe connect to the system?

Another minor problem is that the rads upstairs get warm in the summer when the CH should be off and the DHW is on, persumably it is acting as a gravity system, because there is no valve to shut off the CH circuit.

I would presume the very same thing.

Should I convert to a conventional system controlled by a motorised valve?

You don't have to, but you'd save fuel if you did so.

Should I move the position of the pump?

You don't have to, but will your new boiler have two of four tappings?

If two, then you'd have to remove one pump or move both, with pipework changes in either case.

Should I think about upsizing the flow and return pipes (although the upheaval this would cause would be immense)?

Probably not, but how big is your house, and what's the heat output of your new boiler?

What's the best way to remove sludge from the system?

The most appropriate way depends on how much of it you have in your system.

Has it ever been dosed with a chemical inhibitor?

If you vent the radiators, do you get just water, or some gases first?

Is the water that comes out clear, or dark?

If you look in the F&E cistern, is the water clear, or murky?

Is there much sludge/sediment in the bottom of the cistern (test with finger with system off and then leave any sediment to to settle before turning on again)?

 

[ChrisR]

See the faqs - pumping over.

 

[kildonan]

We have a problem of warm/hot water being PUMPED into the F&E tank via the expansion pipe... .

Do you mean that it's pumped out (a) via the cold feed from the F&E cistern, or (b) via the vent?

It is pumped out via the vent

And do you have separate cold feed and vent pipes, or combined?

Separate

If separate, where does the vent pipe connect to the system?

Approximately ten feet below the F&E tank

Should I move the position of the pump?

You don't have to, but will your new boiler have two of four tappings?

The new boiler (Mistral CKUT3 - 90/120) has arrived and only has a single vent and a single flow connections and the connections are in different positions, so some re-plumbing is required.

Should I think about upsizing the flow and return pipes (although the upheaval this would cause would be immense)?

Probably not, but how big is your house, and what's the heat output of your new boiler?

The house is a six bedroom 200 yearold stone farmhouse in a very exposed location on the Isle of Arran. UFH downstairs and Rads upstairs

What's the best way to remove sludge from the system?

The most appropriate way depends on how much of it you have in your system.

Has it ever been dosed with a chemical inhibitor?

If you vent the radiators, do you get just water, or some gases first?

Is the water that comes out clear, or dark?

Yes, it was originally dosed with inhibitors, but this will have been diluted somewhat over the years. I have drained the system from the lowest point and pumped it through with fresh water for several hours. The water seemed fairly clear and ran clear within minutes. There was some build up of sludge at the lowest point in the old boiler, but not a lot.

Generally, there was little or no air when venting the radiators and I think there are two de-aerators fitted. The F&E cistern has a small amount of sediment.

I have checked out the posts related to Pumping Over and from these it seems like the problem is either caused by a blockage or the pump pressure being too high. The latter seems likely; when both DHW and the Rad circuit are calling for heat then both pumps will be on forcing the water up through the vent.

I plan to connect the new boiler in the same manner as before and see if the problems persist. Meanwhile, I will order a motorised valve and work out how to connect it.

Thanks for your help

Chris

 

[Softus]

If separate, where does the vent pipe connect to the system?

Approximately ten feet below the F&E tank

Um, actually I meant between what and what, rather than a measurement of distance.

In other words, in the direction of flow, what's immediately before the vent connection and what is immediately after it?

Should I think about upsizing the flow and return pipes (although the upheaval this would cause would be immense)?

Probably not, but how big is your house, and what's the heat output of your new boiler?

The house is a six bedroom 200 yearold stone farmhouse in a very exposed location on the Isle of Arran. UFH downstairs and Rads upstairs

If the new boiler has a 90KBtu output, and if that's representative of the the rate of heat loss from your house, then it's possible that you'd need to increase the guage of some of the distribution pipework in order to get the most out of it, but that's a project that can be undertaken separately to the boiler installation and the solving of your pumping over problem.

Yes, it was originally dosed with inhibitors, but this will have been diluted somewhat over the years. I have drained the system from the lowest point and pumped it through with fresh water for several hours. The water seemed fairly clear and ran clear within minutes. There was some build up of sludge at the lowest point in the old boiler, but not a lot.

Hmm. So it's still not clear why it's started pumping over.

Generally, there was little or no air when venting the radiators and I think there are two de-aerators fitted.

Do these de-aerators each have a vent? Are they combined into one single vent?

Also, given the propensity for them to clog up, have you checked that they aren't?

I have checked out the posts related to Pumping Over and from these it seems like the problem is either caused by a blockage or the pump pressure being too high. The latter seems likely; when both DHW and the Rad circuit are calling for heat then both pumps will be on forcing the water up through the vent.

Has anyone turned up the speed of either of the pumps?

I plan to connect the new boiler in the same manner as before and see if the problems persist. Meanwhile, I will order a motorised valve and work out how to connect it.

Bear in mind that you'll need a room thermostat and a cylinder thermostat for everything to work in concert in the most economical way.

If you retain the two pump system then you'll need a method of isolating the pump feeds from each other, but it would be odd if you didn't already have this covered.

 

[advancedplumber]

it sounds more like the pumps are in the wrong position in the system. i'm not going to start explaining this cos we'll be here all night. i have been to jobs where the pump has been in the correct postion and it has still cause this problem which we call 'pitching over' .anyway to keep it short and simple, when i come upon this problem, i convert the ' open vented system' to a sealed heating system. replacing the 5 gallon feed and expansion tank in the loft with an expansion vessel of the correct size. then the problem cannot occur. they say the pump should still be fitted in the correct place but i have never seen it cause any problems so long as the system has been plumbed properly from day one. water also heats more efficently when under pressure. i don't understand what you ment when you said the 'water jacket has failed'???? by the way you can't use this system if you have an open fire back boiler/ solid fuel boiler linked to an oil fired system. if your changing your boiler it would also be advised to put in a condensing model. yes they are more expensive bit with the way oil prices are going they are worth it. i really don't advise anyone to attemt tackling plumbing and heating unless they are quailfied. there are some plumbers out there that are quailfed and they take short cuts and sometimes don't really know what they are at cos they have been badly trained by their employers how pass on bad habits. trust me, i'm a plumber!

 

[Softus]

i don't understand what you ment when you said the 'water jacket has failed'?

Not that it matters, since the new boiler has been delivered already, but perhaps he meant that the water jacket, inside the boiler heat exchanger, is leaking. Either that or one of the host of other ways in which it can fail.

i really don't advise anyone to attemt tackling plumbing and heating unless they are quailfied.

In that case it seems odd that you've joined a web forum whose existence is geared almost exclusively to the giving of a huge quantity of advice to novices on subjects like plumbing and central heating.

 

[advancedplumber]

theres somethings i can safely advise people to do. without looking at something and understanding it fully you can do big damage. if a heating system isn't done right you could have a boiler explosion. and i'm not talking about a gas exlosion. i would like to advise people and help them, but sometimes its very limited to what i can doover a keyboard.

 

[Softus]

i would like to advise people and help them, but sometimes its very limited to what i can doover a keyboard.

In that case I suggest that you put down the keyboard, back away, and leave the giving of advice to people who don't have the difficulty that you do.

 

[kildonan]

If separate, where does the vent pipe connect to the system?

In other words, in the direction of flow, what's immediately before the vent connection and what is immediately after it?

I think the vent is connected to the flow after the boiler and after the branch to the downstairs UFH and before any of the upstairs rads

The house is a six bedroom 200 yearold stone farmhouse in a very exposed location on the Isle of Arran. UFH downstairs and Rads upstairs

If the new boiler has a 90KBtu output, and if that's representative of the the rate of heat loss from your house, then it's possible that you'd need to increase the guage of some of the distribution pipework in order to get the most out of it, but that's a project that can be undertaken separately to the boiler installation and the solving of your pumping over problem.

Because of the exposed location and the draughty original sash windows, the old Potterton Statesman 90/110 boiler could not keep up with the heat loss on windy days, but windy days tend to be the mild ones.

Generally, there was little or no air when venting the radiators and I think there are two de-aerators fitted.

Do these de-aerators each have a vent? Are they combined into one single vent?

Also, given the propensity for them to clog up, have you checked that they aren't?

I haven't touched the de-aerators, they are just before each of the two pumps on the retuns side of the boiler. I will check them next Friday (I'm currently away from home)

Has anyone turned up the speed of either of the pumps?

Both are on minimum

Bear in mind that you'll need a room thermostat and a cylinder thermostat for everything to work in concert in the most economical way.

If you retain the two pump system then you'll need a method of isolating the pump feeds from each other, but it would be odd if you didn't already have this covered.

The system already has a cylinder stat, but no room thermostat (except one that controls the UFH). All the rads except one have TRVs fitted.

Thanks for the help.

Chris

 

[kildonan]

i don't understand what you meant when you said the 'water jacket has failed'?

Not that it matters, since the new boiler has been delivered already, but perhaps he meant that the water jacket, inside the boiler heat exchanger, is leaking.

Yep, that's what I meant.

Chris

 

[kildonan]

it sounds more like the pumps are in the wrong position in the system. i'm not going to start explaining this cos we'll be here all night. i have been to jobs where the pump has been in the correct postion and it has still cause this problem which we call 'pitching over' .anyway to keep it short and simple, when i come upon this problem, i convert the ' open vented system' to a sealed heating system. replacing the 5 gallon feed and expansion tank in the loft with an expansion vessel of the correct size. then the problem cannot
occur.

I think I'm could do this.

by the way you can't use this system if you have an open fire back boiler/ solid fuel boiler linked to an oil fired system. if your changing your boiler it would also be advised to put in a condensing model.

We only have the oil boiler and the new boiler is a condensing one. This means I will have to install the condensate trap and drain, but that's straight-forward.

I really don't advise anyone to attempt tackling plumbing and heating unless they are quailfied. There are some plumbers out there that are qualified and they take short cuts and sometimes don't really know what they are at cos they have been badly trained by their employers who pass on bad habits.

I take your point, and I'm sure the original installation is an example of the scenario you describe (plumbers son turns builder, but still does a bit of plumbing and 'trains' his workmen to do a bit of plumbing - nice guys but their plumbing is innovative). Living where I do, we don't have any choice but to do a lot of DIY. I'd rather get a competant plumber in, but after waiting for 12 weeks through the onset of winter and still no word after many reminders, there comes a time when a man's gotta do what a man's gotta do. With 6 kids and a wife to keep warm, I had no choice but DIY. I understand the dangers and am fairly competant.

Thanks for the suggestion regarding conversion to a sealed system. Actually, I was thinking of installing a Gledhill Torrent thermal store, but that might not solve the over-pitching problem. I'll find out about more.

Thanks

Chris[/quote]

 

[Softus]

I think the vent is connected to the flow after the boiler and after the branch to the downstairs UFH and before any of the upstairs rads

If it is, then high resistance to flow in the upstairs zone could result in pumping over. The remedy in that situation would be to move the vent to be upstream of the pump(s).

Because of the exposed location and the draughty original sash windows, the old Potterton Statesman 90/110 boiler could not keep up with the heat loss on windy days, but windy days tend to be the mild ones.

Eeek!

I haven't touched the de-aerators, they are just before each of the two pumps on the retuns side of the boiler. I will check them next Friday (I'm currently away from home)

Hmm. That's perplexing. Where does the the air from the de-aerators go?