Heating System Pushing Hot Water into the Expansion Tank


Postby gos9 » Tue Jan 13, 2009 3:24 pm

Hi

I have recently had a new Glow Worm boiler fitted to a two pipe vented system.

I am having to run the pump on setting 3 as when I switch to setting 2 the boiler immidately shuts down. On 3 I am getting hot water going up the expansion pipe into the tank and both the 15mm supply pipe and the expansion pipe get to hot to touch and my loft is full of condensation.

This problem seems worst when the hot water cycle is operating.

I have had the system power flushed on two occasions and had a Boiler Buddy fitted which is showing clean water in the system.


Can anyone help before I spend more money on the system.

Thanks
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Postby swidders » Wed Jan 14, 2009 12:03 am

Three solutions spring to mind-
1/. (most expensive) - see if you can get a pump with different flow rates since your one is either too high or too low!

2/. change the pipe layout to the expansion tank so the bottom pipe becomes the overflow and vice-versa. this will mean that the pump will try to force the water up the other pipe and it's possible that the installers connected the overflow pipe to the flow instead of the return, thus there is a greater pressure from the pump pushing water up at this point. Sounds odd, but have come across this a couple of times and it has been known to work.

3/. you could try to put an isolating valve on the overflow pipe (the one that goes into the top of the header tank) and turn it so it is still open, but not so much. this will allow for expansion but increase the pressure in the pipe enough to hold the water down. not a well known method but is one you could try using a speedfit and a pipe slice if necessary.

Needs to be sorted soon, since high temperature may well distort the tank and cause it to fail, thus giving someone below a very unwelcome surprise - there was a case a few years ago where an infant in the bedroom below was scalded to death!!!

Will probably be slated by other plumbers for these - but luckily they don't know where I live!!
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Postby moonguy » Fri Jan 16, 2009 5:52 pm

[quote="gos9"]Hi

I have recently had a new Glow Worm boiler fitted to a two pipe vented system.

I am having to run the pump on setting 3 as when I switch to setting 2 the boiler immidately shuts down. On 3 I am getting hot water going up the expansion pipe into the tank and both the 15mm supply pipe and the expansion pipe get to hot to touch and my loft is full of condensation.

This problem seems worst when the hot water cycle is operating.

I have had the system power flushed on two occasions and had a Boiler Buddy fitted which is showing clean water in the system.


Can anyone help before I spend more money on the system.

Thanks[/quote]

Hi

Did you find the answer to your problem, if so what was it?

My Baxi stopped working last night, thought it was the pump, but then found no water getting to the pump. Quick bang on the pipe near the pump un blocked it. Fluched it all through etc and now heating working fine. But when I turn the hot water button on on water runs back up into the expassion tank. The one thing I found interesting in your subject was that you run on setting 3. I always run on setting 1 or 2. But I was told it should always be on 3. Its on 3. I will in the morning try and run heating, pump on 1 or 2-see if this stops the problem, unless it's the gate valve? anyother ideas or anyone??

Thanks

Neil
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Postby DEEARR2 » Fri Jan 16, 2009 7:46 pm

Sounds to me that the pump is fitted incorrectly in relationship to the system and the expanssion. Have who ever changed the boiler check this out.
Way of the mark SWIDDER with the fitting of a valve on the expanssion pipe as this does not comply with acop and could be dangerous. ( not recommended)
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Postby Cav » Sat Jan 17, 2009 3:26 pm

[quote="swidders"]

3/. you could try to put an isolating valve on the overflow pipe (the one that goes into the top of the header tank) and turn it so it is still open, but not so much. this will allow for expansion but increase the pressure in the pipe enough to hold the water down. not a well known method but is one you could try using a speedfit and a pipe slice if necessary.

[/quote]

What kind of idiot would advise this? NEVER put any kind of valve on the vent pipe, this is a vented system not unvented...this contravenes the building regs and instead of failure of the F&E tank, you could end up rupturing the cylinder

On the problem at hand, it sounds like the pump is fitted the wrong side of the vent pipe and the system is pumping over, both the cold feed and vent should be on the end of the system at the neutral point

The vent pipe should be connected at the lowest possible pressure and within 150mm of the cold feed pipe...but before it!

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Postby swidders » Sat Jan 17, 2009 10:26 pm

Ref : valve on vent pipe

Oops - wasn't aware of regs and potential damage. Got this solution from a plumber with 25+ years experience who i worked with a few years ago. I questioned him at the time and he told me that since the valve was still open, then it was still a vented system but could be adjusted to emulate a higher head on the overflow.

Don't know who taught him this technique, but thanks again for the correction - luckily I haven't used it to date, and now will be sure not to!!
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Postby TheDoctor5 » Fri Jan 23, 2009 9:30 am

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