Customer complaint: older Dunkirk boiler, pilot went out, he removed and cleaned the pilot assembly, reinstalled, lit pilot then observed main burner light. As he was putting covers back on, he jostled the thermocouple line and the pilot went out. Subsequently, after relighting the pilot, the main burner would not light.
I diagnosed the Hydrolevel 3250 controller as failed and replaced with new, but the same thing happened as I was putting on the covers. Contacted tech support and was told to replace the new controller under warranty. This time I checked and tightened the slightly loose thermocouple into the gas valve. The boiler has worked normally since. Note: the problem with the failed controllers was at the gas valve relay providing 24v to B1 & B2 on the printed circuit board. How would the loose t-c cause this?