I have a empire wall heater model # gwt-35-2 . 35,000 BTU. I have replaced the thermopile with a robertshaw # 1950-001 thermopile 36" 250-750 millivolts, 2 lead type. Have also replaced thermostat with Honeywell # CT33A compatible with millivolt heat only systems.Two years ago I replaced the over heat control switch& thermostat wires.
The problem is the heater only stays on for about a minute. Turns off then comes back on about 10 minutes later . Stays on another minute and so on.