Combi boiler (Baxi 100HE), when I set water pressure to approx 1.75 bar I get some water escaping from the external pressure relief valve, maybe half a cup or so. Anything below 1.75 bar is ok. Is this normal or should I be checking anything else. Central heating works ok
Heating, pressure relief valve
May 09, 2017
4 Replies
It is not normal
I suspect that is cold pressure and its shooting up when hot
Indicating a pressure vessel that has failed or needs recharging.
Or the pressure relief valve may be faulty instead
It's not normal.
1.75 bar sounds quite low. Something like 3 bar would be more like it. Does the pressure relief valve state its operating pressure?It's generally not good for the PRV to operate, as IME they often don't re-seat properly and you can end up with a slow drip all the time.
Does it escape as soon as you pressurise the system, with everything cold, or only after it heats up?
The PRV should operate at 3.5 bar so if it operates at 1.75 bar, it's faulty.
If it only operates when hot, it means that the pressure is rising above
3.5 bar when the water expands. In that case, the expansion vessel could be shot - or the system could just have insufficient expansion capacity.A static pressure of 1.75 bar sounds a bit high - 1 bar would be more normal. If it works ok by using a lower static pressure, it's probably ok.
+1
In my experience, once the valve has started leaking it is likely to continue, either because of erosion or deposits on the sealing face. (That said, on my latest boiler I did get a relief valve leak after the filling valve started leaking, but it seems to have survived that).
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