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drop in pressure on boiler

Postby mohs33 » Thu Jan 13, 2011 1:58 pm

Hi All.

I am new to all this so bear with me.

I have a Vailiant combi boiler. It always stops working and the hot water and heating go cold. I have to refill the boiler and re-ignite the flame. This is a regular occurance now (daily).

It leads me to believe that it could be a leak somwhere, am i right? in the house, but i cant see any damp patches or water anywhere, which has left me very confused.

Can anyone advise?

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Postby stoneyboy » Sat Jan 15, 2011 4:33 pm

If you can't find a leak it could be that your pressure vessel has failed.
Once you have refilled the boiler, turn on and see water comes out of the safety valve overflow - may take a bit of time while the system gets hot and expands.
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Postby mohs33 » Sun Jan 16, 2011 2:52 pm

Hey stoneyboy.

First of all thanks for the reply. I've checked the overflow pipe and it is releasing water. Also it seems like there is a slight leak coming from inside the boiler. After doing some reading around all the signs do point to having a problem with the expansion vessel

Many thanks
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Postby htg engineer » Mon Jan 17, 2011 9:59 pm

If pressure rises to above 3 bar, then yes it could be the expansion vessel. Check combi fill is turned off, you could also turn off cold mains to boiler, if pressure still rises this rules out pin-holed plate heat-ex.

If pressure stays below 3 bar - could be faulty pressure relief valve.

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