Strange drop in pressure from boiler.

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Argyll
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Strange drop in pressure from boiler.

Post by Argyll » Wed Jan 10, 2018 10:24 am

I’m having some problems with my boiler just now.

It’s a Potterton Combi HE 33kw. It’s been losing a bit of pressure recently. I have the radiator off in the hall just now because I’m decorating but I don’t think this would be causing it. There does however seem to be a leak on the floor underneath the boiler but this seems to be coming from the condense pipe before it goes into the wall. I intended to repair this myself this weekend but would a leaking condense pipe cause a drop in pressure?

Last night I returned from work about 18:30 and noticed there was no heating on. The pressure gauge was almost at zero. I jagged it up to about 1.5 bar in the green zone and the heating came on. Several minutes later the gauge was well in the red zone. I know the pressure jumps up when the heating pressurises but this seemed to be excessive. I bled one of the radiators to bring it back down to a safe pressure. The heating worked well and went off at 22:00. However it didn’t come on this morning and the gauge was almost at zero again!

There’s no obvious leaks on the radiators and I can see no evidence of leaks in the ceilings. Would the leak from what appears to be the condense pipe be the culprit?

A Homeserve engineer is coming out this afternoon but I’m just curious what the problem could be.
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Re: Strange drop in pressure from boiler.

Post by gas4you » Wed Jan 10, 2018 1:00 pm

The condensate pipe in itself will not cause any pressure drop, however, in the unlikely event that the main heat exchanger is pin holed, then the system water will leak out via the condensate pipe, but you should not be seeing any water under the boiler whatever.

The expansion vessel could be flat so when the heating comes on the pressure rise to over 3 bar then the safety valve opens and dumps the water outside via the 15mm copper pipe.

Make sure he drains the boiler and checks/re-pressurises the expansion vessel whilst there. A bit of a pain on these boilers if, like me, you have big hands!
Dave

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Re: Strange drop in pressure from boiler.

Post by Argyll » Fri Jan 12, 2018 12:18 pm

You were spot on. It had something to do with the expansion vessel. He attached a foot-pump to the top released a valve at the bottom and forced out the water. He then pressurised it and it seems to be working well now.

The condense pipe was cracked so he's has temporarily disconnected it for now so I need to empty a bucket every other day. He didn't have the 90 degree bend fitting so he needs to return to repair later.
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