Expansion Valve dischargin

2 Mar 2009
Reaction score
United Kingdom
Pressure relief valve (expansion valve) (twist top type) sometimes discharges water intermittently.

The expansion vessel is to to correct pressure charge. So why this?

The pressure reducing valve has been tested to be ok as max bar water pressure from sink tap is 3.5 bar , and sometimes not even that, so it is working properley.

Is the valve istself just faulty? How can i check this for sure and remedy it? Can I clean it up??

Curious as it is annoying and wasting water and I am on a water meter here.

Any ideas
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Kane: if the pressure reducing valve is fine and the discharge is all the time and not just when heated (charge pressure is OK as you said) then it must be the pressure relief valve is not shutting off properley/not seating correctly. Maybe grit in it (although the line strainer should have dealt with this).

Don't know what else it could be... but you need to be G3 qualified to be able to legally change these parts ... so best calling a plumber who is qualified in unvented hot water to do it for you
There is probably no expansion space left. You haven't said much about your system, so you won't get much advice as to what to do.
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could be caused by mixer taps with no check valves fitted.or taps mixing hot water with unbalanced cold water which could result in cylinder back pressure.

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