Gas Furnace startin problems

[IA Roy]

I have an older gas (propane) house furnace in my shop. Lately when I turn the switch on the thermostat to on, nothing happens. There is no click at the furnace. If I repeat the operation, it may or may not kick in. Any thoughts on this. I have not checked to see if it is getting a voltage signal to the valve. I don't think it would be the thermocouple as I believe that only controls the pilot light.
Thanks for any suggestions in advance.
Roy
 

[old]

Good chance you have a relay going bad and that click you here is it doing its thing. You can have some one t8urn it on and off while your close to find it by sound or of course you can use the wiring diagram if it is still there
 

[Greenday]

Could be a bad sub base on your thermostat
 

[rd 2N in mo]

I just replaced the computer panel on a 1989 lennox that would start and cycle thru for 4 or 5 minutes and then shut down. It would not get up to temp and the repair guy came to check it out. he was here for an hour and could not get it to fail. finally got it to fail and replaced the 23 year old motherboard and it runs great now
 

[George Marsh]

You mentioned old and thermocouple, so does that mean you have a standing pilot?

If so, then the theromostat only sends 24 vac to the gas valve. Measure the voltage to the gas valve. By turning the thermostat on and off many times, its a good guess you have an issue with the thermostat, thermostat wires, or a sticky gas valve. Measure voltage at valve and tell us more about furnace.

If you have a high efficency gas furnace, then you may have many issues. Need more info.

George