In article ,
"DavidM" writes:
(yes I know it's 35 years old and needs replacing - I'm just trying to nurse
it through until spring!)

The boiler is overheating (radiators too hot, HW scalding and boiler
creaking a bit). The room and HW cylinder thermostats are working ok, so I
thought the problem was the boiler thermostat. Replaced it with a new one
last week but problem still persists. If I turn the boiler thermostat down
to zero it clicks off and the boiler shuts down, but putting it to any other
setting from 1 to 6 the boiler just keeps going until the room/cylinder stat
shuts it down. Turning the knob through it's range there's no feel/sound of
it switching as I'm sure the old one used to do. I suppose the new
thermostat could be faulty - any way of testing it?

What sort is it? Does it have a phile on the end of a thin
copper tube? If so, test it by dunking the phile in a mug
of hot water with a separate thermometer. The temperature
range from min to max should probably be something like
60C through to 80C or 85C.

--
Andrew Gabriel