Sitting in my kitchen tonight I turned on the heating, nothing happened (i.e. usually I hear it 'kick' in) so I switched on the 'valve' ( that expels the air?) and I heard running water - opened the kitchen door (combi boiler on the wall just inside) and saw water running out of a small pipe near ground level I've never noticed in 15 years! Water was running out. It stopped. No action from the boiler. I left it switched completely off just in case. What do I do next? Clearly no hot water or heating. What should I do?
Irene

Irene Murphy, April 2011

You tried to top up the system by letting water in. The pressure got high enough to operate the system overpressure relief valve, at around 3 bar. If you are regularly topping up it is very likely that you need to recharge your expansion vessel. Whilst you could do this yourself, it is not difficult, just need a car tyre type air pump, there are no gas safety elements and you can google the instructions., you might prefer to get a gas man to do it (will cost you -may try to tell you its obsolete, cant be fixed, need a new one etc)


Watch the system pressure as the central heating goes from cold to hot - if it increases much you do need to pump the vessel up.

The overflow is the normal, safe, response to what you did (over pressurise the boiler). Dont worry.

c#, April 2011