Hi, I have a problem with a potterton profile 30 boiler, the fan comes on then switches off, it does this forever without the ignition firing up or any sparking taking place. So I remove the front cover and the fan runs continuosly, then i put back the front cover, I have to do this for some time then it will just start up and work fine until the timer switches it off, then I have to do the whole process again!! Any ideas anyone?? I've changed the air pressure switch so its not that, thanks in advance Spidy