Combi keeps cutting out

[PC Paul]

My Myson Midas combi keeps cutting out (pilot goes out). A plumber came a while ago and replaced the thermocouple and it seemed OK for a bit, but now it's doing it again.

It *seems* to be that it fires up when the tap goes on, but doesn't switch off again after, leading to it overheating and presumably a safety trip cutting the gas.

Could it be a sticking pressure switch? When they fire up should they cut off again as soon as the tap is off, or do they run on for a while for some reason and get switched off some other way?

Also, the plumber mentioned that it was an old boiler and hard to get spares for now. Any truth in that?

[John Rumm]

IIRC the Midas has a small internal store of water (i.e. under 10L) so as to give "instant" hot water. So you may get a small amount of run on as it re-tempers that.

They do have a very sensitive flow switch however (leave a tap dripping at it will lock the boiler into hot water mode and kill the heating), so it could be what is wrong with yours.

Old, yes (my mum had one installed about 20 years ago). Not sure what the state of play on parts is... (cue Geoff!)