Central Heating Woes

[Capt T]

Got in last night and the boiler was thrashing away as usual but the radiators and hot water seemed very hot. Suddenly an overflow started going and it was all steam and hot water. This is a basic gravity fed system hot water tank upstairs potterton kingfisher floorstanding boiler downstairs.Boiler renewed 15 years ago tank never. In the loft it looks like the hot tank has " vented " into the small heating tank and made it overflow. This has never happened before. I turned everything off and this morning on a low boiler thermo setting things are working although we do seem to get a fair bit of background banging sounds when the boiler is running. Is this bad news or a one off? What can I check or do? Is it safe?

Any ideas gratefully received.

[Andrew Gabriel]

Sounds like the boiler thermostat has failed, and it boiled the water. This should be quite cheap and easy to fix, although I don't know that boiler model.

It's not safe running with a faulty thermostat. There is a case where someone was killed when the header tank eventually got to boiling point, and being a plastic tank not designed for this, it collapsed and poured the boiling water through the bedroom ceiling. In this case it was the immersion heater thermostat and large header tank, but the same could happen with the smaller one.