I have an ARCO Air forced air gas furnace model GHA075NDC. The pilot light stays lit and the fan comes on when I put the thermostat to fan on but the heater will not ignite.
I need heat this winter. Please help!!

Pattyg if your trying to trouble-shoot the furnace yourself use Northernheat's post from years ago.


https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-faq-northerheat-58313.html

I couldn't fine anything with that model # but I would look at changing thermocoupling (cheap and easy), and cleaning flame sensor if it has one. Good luck

If the pilot stays lit, the thermocouple is not the problem & there is likely no other flame sensor. If you have a voltmeter & know how to use it, check for 24 volts ac at the wires on the gas valve. The thermostat must be set for heat & turned up several degrees above room temperature when testing.

I decided to replace the thermocouple even though the pilot stayed lit and the furnace works now!! I replaced the thermocouple over 20 years ago so I guess it was time for a new one.

Just curious as to what else you did to correct your heat situation?

The fact the pilot stayed on yet the thermocouple was bad really makes me question the gas valve. What would happen if the pilot went out? Would gas continue to flow?

Grady, you bring up a good point, I've seen this more than once where a change in thermocouple would get the furnace up and running. What would you do to check the valve?

Blow out the pilot, give it 15-30 seconds & try to relight the pilot without depressing the pilot button. If the pilot lights, the valve has to go.

Thanks Grady, I'll use that test next time I run into this, I thought the thermo's just got to weak to work the main valve.


I hope Pattyg sees your post.

The thermocouple only operates the pilot valve, unless we are talking about a power pile i.e. millivolt gas valve.