i have a potter ton kingfisher mf. It is sometimes locking out. It also makes a clicking sound before firing up. Sounds like a relay which clicks twice sometimes 5 times and repeats until it fires up. Adjusting the main temp knob varies the speed at which this happens. Just after the first click it also sounds like the fan tries to start before stopping. While this is happening I do not see the pilot light spark up. Although I can't be sure it also only seems to happen with hot water not CH. Any ideas? Thanks