My Potterton Prima F boiler keeps igniting then going out?

The circulating water pump is not working. This causes the boiler to turn off with over-temperature. Or the boiler themostat is faulty, but you say the casing is very hot so this is probably not the fault here. I had the same problem. Do not be confused if the pump feels as if it is running. Mine has sheared off the impeller. The water pipes should feel hot on BOTH sides of the pump. Hope this helps

Barry Galvin
March 2010