Gas furnace blows with no heat

Old 11-30-16, 03:44 PM
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Gas furnace blows with no heat

Here's the details of my problem:
- Home/HVAC system just 3 years old
- Temperature switch activates heater fan when drops below certain temp as it should
- Ignitor still has continuity
- No flame when heater is 'on'
- HVAC control circuit says there are no issues (flashing green LED)
- Gas valves and switches are all open/on
- Gas cooker downstairs still works
- I cannot smell gas coming out the furnace

What would you all recommend I look for next?

Thanks in advance!
Old 11-30-16, 04:00 PM
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Welcome to the forums.

Did you check for a trouble light on the control board ? Many furnaces have one that can be seen in a port in the blower door.

It sounds like your draft inducer is starting but the igniter is not. That could point to a pressure switch not activating. That could be confirmed by a trouble code.

A make and model of the furnace is always helpful too. You'll find the info on an ID tag inside the furnace near the burner.
Old 12-01-16, 09:40 PM
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No trouble light.
Furness is a model number GG9S080C 16MP11A. I can't see any brand name on it.
Old 12-02-16, 11:52 AM
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There are two fans in the furnace. A big fan circulates air around the house.

A small fan, usually located above the burners circulates combustion air into and out of the furnace. That's the inducer motor, and it's turned on when the thermostat calls for heat. I presume that's the fan that's turning on?

When the inducer motor comes up to speed, the pressure switch should close which in turn causes the hot surface ignitor to heat up if the furnace is working properly.

So as PJ Max suggests, the likely reason for the furnace not to heat is that the pressure switch is failing to close, usually because of some obstruction in the combustion air flow through the furnace.

Another likely cause of the problem is that the fitting the rubber hose goes into on the inducer motor housing can get plugged with junk and debris, and needs to be cleaned out with a small drill bit.

Use a multimeter to see if the pressure switch is indeed failing to close when the inducer motor comes up to speed.
Old 12-05-16, 01:11 PM
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I had a new controller board put in my furnace after the old one burned badly (Carrier furnace). It got a 3A fuse that blew. The instruction for it said the fan would continue to run when the fuse blew. The fuse was to protect the high current in the secondary something something ...
If there's a fuse on your furnace controller, check it. If it's blown, it's likely the gas valve got a short in its solenoid to give no gas when the last cycle of the system occurs.

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