"Dave Plowman (News)" wrote in message
...
It does indeed sound like the overheat stat has failed, and shouldn't cost
much to have replaced on spec, even although it appears to work sometimes
- like when the engineer calls.

But you could just turn the boiler down initially to perhaps 80C or so -
it doesn't need to be full up for just heating the water.

Thanks Dave. It was, actually, on a lowish temperature setting already (and
50 to 82 degrees is allegedly the control range).

I have investigated further my looking at a parts list in the installation
manual, and the temperature control systems seems to be a little more
sophisticated than a straight old-fashioned on/off thermostat, using as it
does, a thermistor sensing element, and a potentiometer which are connected
to an electronic control board. As BOTH functions seemd to be dodgy (temp
control AND overheat) it might be something as simple as one (or more) of
those grotty spade connectors that has corroded over the years. I'll ask my
man when he comes to remove and replace the connectors a couple of times.
Can't do any harm and may do some good!