Combi letting by through overflow.

[chainsaw_masochist]

A friend of mine called out an engineer to deal with a problem Glow-Worm combi that was providing neither HW or CH. The guy removed the heat exchanger and gave it a descale, replaced it and the boiler worked fine for a couple of days and then failed again. The same chap returned saying the gas valve had packed up and would require replacement so a new gv was installed. The boiler is now operating correctly but there is an occasional dripping from the outside overflow.

What is the likely cause, here? Any advice much appreciated.

 

[McCombi]

Pressure relief valve is passing water to outside.
Whether it's activated as expansion vessel is flat and boiler pressure has risen to 3bar, thus opening valve as a safety measure or whether engineer had used valve to empty boiler when doing previous repair and it hasn't seated properly due to dirt, who knows..

 

[JohnD]

the pressure gauge on the front of the boiler will give some clues. What is the pressure (a) cold and (b) hot?

Does water drip out when cold, when heating up, or when hot?

Are you sure it is dripping from the bent pipe, and not from the flue?

 

[chainsaw_masochist]

Thanks for the useful replies, guys.

I am unable to answer your question re whether this happens when off, on etc , John, as the said flat is in a different part of London to where I am. But the dripping is coming from the vent pipe not the flue.