18 ) WATER IS COMING OUT OF BOILER'S "PIPE" Thanks To ChrisR
Combis (and other boilers) have a metal Pressure Relief pipe going out through the wall, sometimes wrongly referred to as the boiler's "Vent" or "Overflow". For safety it is usually turned back to the wall or taken to a low level. This is the
Pressure Relief Valve and is an important safety feature. PRVs in boilers nearly always have red tops. Old Vaillants are grey.
It can be seen leaking water because:
1) The PRV has been opened (perhaps to let water out of the system) and it has failed to shut properly. This is because dirt gets stuck on the valve seat. You can try to twist the valve and it may "clunk" shut but it can make the leak much worse.
2) System pressure has gone above 3 bar and the valve is doing its job releasing boiler pressure. This is often due to the boiler's pressure vessel needing attention.
3) The pump may have failed.
ANY Pressure Relief Valve which has let water out is likely to need replacing!
Water coming out of a white PLASTIC pipe will be from a condensing boiler and is normal. It must go to a drain and not allowed to dribble on the ground!