Pressure rise on the heating side of a 30cxi combi boiler

13 Dec 2008
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United Kingdom
Hi ,I have a question on a problem my sister in law has on her 30cxi boiler.
The water pressure rises all the time when the heating is on till it reaches 3 bar then the safety valve works and reduces the pressure for the cycle to start again. Would this be a problem with the Pressure vessel or the themistor on the flow?
when the heating is off and the boiler is repressured at 1.1 bar it remains constant.

hope someone might have the answer
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the pressure vessel is more likely to be the fault. any water discharging out the back through the safety pipe?
Yes there was but a new one fitted,
Still discharging though, I will have the pressure vessel checked. thanks for the advice
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ask the eng why he changed the prv wtihout checking nthe vessel. this has cos t more labour and parts than it should have. :confused:
Yes there was but a new one fitted,
I'm assuming you meant new pressure vessel. If so then as stated it needs pumping up.
If you meant pressure relief valve then it is likely that it has been wrongly diagnosed.
Pressure vessels for these are rather expensive. I know because I fitted one on Friday. Unfortunately there wasnt a suitable location for an additional PV which would have been a cheaper fix at less than £40 for all the parts

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