Problem with Ravenheat 820\20 combi boiler

[faulty]

When the hot water taps are turned on the boiler fires up, produces hot water for a couple of minutes and then switches off. It fires up again after about 45 seconds before switching off again. This cycling continues. A similar event occurs on the central heating circuit. The boiler fires up and the temperature dial shows the temperature going up to 50 degrees C before cutting out. When the temperature drops to about 30 degrees C the boiler fires up again. This cycling continues. Altering the temperature controls for radiators or the hot water has no effect.

This may or may not be relevant, the diverter valve was changed about 18 months ago and since then this problem has gradually got worse.

Any help on shedding light as to what's causing this is greatly appreciated.

 

[Slugbabydotcom]

CH thermistor is number one suspect. And from experience make sure the boiler is cold when you change it.

Edit>>>

It may be a CH thermostat on these earlier models. Also worth checking the flue and venturi for obstruction

 

[faulty]

Thanks for the help. I'll let you know how I get on.