Central Heating System Overflow Dripping

31 Aug 2004
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United Kingdom
I have a Potterson (Puma) wall mounted, fanned, electronic combination boiler about 4.5 years old. Came back from holiday to find the pressure level on 4, and my neighbour said the overflow pipe had been dripping for 4 days. I reduced the pressure by bleeding some radiators. The heating system works alright, but the pressure level keeps dropping below 1.0 now, also the dripping continues from the overflow pipe. When the heater is turned on to warm the house, hot water drips from the overflow pipe otherwise it drips cold water.

Please give me an idea of what may be wrong before I call an engineer.
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Presumably you didn't leave the heating on when you were on your jollies. If so, it sounds like you may have had a problem with the filling loop passing or you left it open, raising the system to mains pressure.
This has caused the pressure relief valve to open, (drips from overflow/warning pipe). As is often the case with pressure relief valves, once opened they then do not re-seat properly and have to be replaced.

Hopefully thats all thats needed, a new PRV and disconnect filling loop when not required, (cap ends on pipework).
Thanks for your quick response Leafy. Could the Pressure Relief Valve be replaced under an hour by a competent engineer?
Yes, under an hour. Also its important to check the pressure in the expansion/pressure vessel. If its too low ( not anough air) the vessel will fill up with water so there will be nowhere for expansion to go when the water gets hot - except through the pressure relief valve.

Both jobs together , and pump to proper pressure, under an hour.
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Switch off your water next time you go on holiday, I always put my gas and water off, but then I am a clever sod.

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