alright, big heater in the shop is acting up… it’s a large gas furnace. thermostat on the wall, transformer on the heater, pilot light is on, you can hear the click of the thermostat but no action. three terminals on the control TH, TH-TR, and TR, one wire from the thermostat goes to TR, the other thermostat wire goes into the transformer and comes out to the TH terminal.
any suggestions on how to bench test or verify what could be acting up?
thermal coupler
yeah, been looking online for info when i threw this thread up. hit the gas valve with a hammer and we now have heat…
was just going to say, gas valve. see if it has voltage but wont turn on. ours just went on the furnace, ~$300
replaced mine (called Auto Valve) myself ($170) after RG&E had red tagged it for leaking from the switch. Learned a lot about boilers and gas lines (they had red tagged a pipe elbow too).
I didn’t think to fix it with a hammer though. maybe next time. 
didn’t exactly haul off and beat it… just a tap with my little hammer and it fired up, might be a sign that it’s about to crap out.