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Boiler Pressure Relief Valve Pipe – aka what is that small metal pipe sticking out of my house leaking water?

A slightly leaking Pressure Relief Valve exit from a Combi-Boiler through a brick wall

If you have ever wondered what bit of plumbing a small metal capped pipe that sticks out of your house could be, then that is the end of your combi boiler’s PRV (Boiler Pressure Relief Valve): and if it has water dripping/leaking from it, it most likely means your boiler has been over pressurised (i.e. you’ve put too much water in it) or you may have a faulty expansion vessel in your boiler.

Luckily for us, this isn’t our pressure relief valve pipe – but I did initially think it was (as it was on “our side” of an exterior wall).

The pressure relief safety valve (PRV) is mandated by British Standard BS 6798:2014 for sealed central heating systems and is intended to stop any excessive pressure causing damage. The small pipe bit isn’t actually the valve itself, but is just the pipework which leads from the spring-loaded valve within the boiler. Leaks from it could also be caused by the valve not being able to close correctly due to dirt build up.

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