Hi, I have an Ideal wlx boiler, It will fire up on requesting both hot water or heating but makes what I can only describe as a rotating fan sound, then the flames(not the pilot light) cuts out after a few minutes. I'm wondering if it could be the boiler thermastat as it fires up for longer periods the longer it's left, for it to cool down?. Any advise would be great thanks. p.s The 3 way valve appears to be working fine.