Potterton Performa 28 Lockout

COVKID

I have the above boiler in my garage.There is a frost thermostat fitted to wall next to boiler.I notice from literature there is an integral frost protection system which operates if the temp.falls below 5 degrees then the boiler will fire on it's minimum setting until 30 degrees is reached. If this happens i have an electric fire which i switch on ( to save the heating being on all night),when it is warm enough the boiler switches off .This has worked alright up until this week,when the boiler would'nt work.Pressing the re-set selecter the pump and fan work and the ignition clicks for 10 seconds but no light up.
this happened exactly the same last week but after some general tinkering about after about 30mins.it suddenly fired up,no such luck this week.Anyone had any similar problems or could suggest where the fault is.
Thanks

Skiduck

check air pressure tubes for splits. if no splits, if all ok possible faulty air pressure switch or pcb board