boiler fires warms water then locks out saying f3 fault "boiler overheating " what could this be ? blocked heat excanger or diafram ?

c phillips, July 2008

First place to try would be the circulating pump. 90% of the time Overheat faults are where the boiler is not dispersing the heat quick enough. A blocked heat exchanger is a more drastic fault and highly unlikely due to the age of the boiler. There may also be a thermostat or board fault but these will need to be pinpointed and fixed by a Heating engineer.

Steve, July 2008