Hi guys. I have a Potterton Prima F50. Normally when there is a call for hw or ch i have the flame going off after the boiler has run for 5-10 minutes. Then i hear the click of the fan attempting to switch itself on several times before the boiler relights again ( i suppose the boiler goes off because the thermostat reaches the set temperature and when the boiler temp drops it relights again and during that time the fan goes on and off probably because it is still receiving the call for heat.). Last week though, the boiler went off after 5-10 min but the fan carried on running non stop for about 20 min while there was still a call for hw, but the boiler refused to relight. I tried the reset button underneath the boiler but nothing happened. I reached the programmer and switched the hw call button on the programmer ( which i leave it on all the time) off. That stopped the fan running. I switched the hw button on the programmer back on and the boiler relit. Since then i have had no problems but this morning that problem occured again and i did exactly the same thing that i did last week and it worked again. I know it is not normal and before that trick stops working i would like to know what might cause that erratic behaviour. Can anyone point me in the right direction? Thank you very much for your time. BTW i have had a contract with BG for the past 5 years for servicing it and cancelled it last summer.....how typical