I had a new Promax HE 150 installed about 5 months ago and have had loads of problems - including error codes Potterton don't recognise. Potterton have been out 6 times, replacing the PCB 3 times and the entire top half of the boiler once. It is supplying CH through radiators to the main house and underfloor heating to a new extension so has had two seperate time clocks installed. The boiler keeps igniting - reaches temperature within 2 mins then shuts off. Temperature immediately drops within 2 mins and reignites. This goes on continuously.

treehouse, January 2008

It sounds like the water is not being circulated out of the appliance quick enough... Possible issues with the pump or diverter valve, something restricting the flow from the appliance and around the system/systems it is supplying ... The water is being heated to the required temperature then shutting down because it is satisfied only to be replaced with cold again hence the 'cycling'....

DiamondGas, January 2008