I fitted a new fan, and everything worked great for about 2 days. Then disaster. The spark igniter did not spark, so no pilot, no burner. All indicator lights come on the PCB, and, if I use a match I can light the pilot manually, and it will work, main burner comes on, but, no self ignition. Can anyone help please? Is it PCB, or some other obscure bit which I havent found out about yet.