Flow sensor, PCB or something else?

[andydona]

Hi. I have a 10 year old Glow worm Ultracom which has regularly started "thinking" there's a demand for hot tap water when there isn't. It frequently fires up for hot water, sometimes after a cold taps been used but more generally with nothing obvious to trigger it (no tap/toilet/washer etc in use) I heard it fire up at 4am the other morning. Glow worm technical think flow sensor or PCB. Another forum suggested a dead leg with trapped air. This sounds reasonable if there's a trigger (cold tap, etc) but generally there's nothing in use, plus the pipework, etc hasn't been modified in years, so why now? I'm happy to go for Glow worm's fixed price repair if it's likely to be the PCB but it would be a lot to pay for a flow sensor swap. We've had 2 die in the past, but in both cases they simply died. They didn't cause this type of problem. Any thoughts gratefully received!