On Sat, 31 Mar 2007 14:21:42 +0000, Denn013 wrote:

The overheat cut out has started to operate on our Potterton Prima 40F gas
boiler. It restarts and operates fine after resetting the cutout after
allowing time for it to cool down. This happens a couple of times a day.
Does this mean the boiler thermostat needs replacing? or could there be
another likely cause?

Could be lack of water to the system. Are the upstairs rads hot all the
way up? (see
http://wiki.diyfaq.org.uk/index.php?...Heating_Repair)

If you turn down the boiler thermostat does the overheat cutout still
trip? Does the flow pipe get much too hot to touch? At Max on the boiler
stat it should get to about 80C, that's as hot as the rad on your car, and
hot enough that you can't hold it for more than about a second with dry
hands. With the boiler stat lower it should be cooler: if it isn't then
maybe the boiler stat's not working (when you turn it down the boiler
should stop). If The cutout is going with modest flow temperatures than
the overheat stat itself may be faulty.