I have an Amana furnace GUCA 070 AX30 furnace installed in 2002. My original installer has retired. The last two nights the blower goes on at 3:30 am when the house is 70 degrees and the thermostat is set at 67 degrees. The blower runs a few minutes then shuts off. I shut off the power to the furnace then at 6 am I turn it on. The blower comes on immediately but the ignitor does not power up. I get 5 flashes on the failure code led. I turn off the power for a second and turn it back on and I get a normal furnace start-up and heat. The current Amana dealer says sometimes the blower just detects warmth and turns on. The basement is 65 and the outside is 50. This doesn't seem reasonable to me. Any suggestions on what the problem is? Thanks

How old is your thermostat? It is in heat mode when doing this?

Yes, it is in heat mode. I changed out the thermostat to a new one between the two nights and it did the same thing with both stats. Both thermostats are Lux TX9000TS models.

https://manualzz.com/doc/11060...0ax30-specifications

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Are you getting a flame? At what point does it stop? If no flame, check induction motor or vacuum switch. If those are good check hot surface ignitor. If you get ignition, but the furnace shuts down after 30 seconds, it's likely a flame sensor which can be fixed by scrubbing it with a dry green scotchbright pad.

Can you see the ignitor glowing? Do you have a multi meter that can read resistance?

The issue is the blower coming on in the middle of the night when no heat should be required. When I get up in the morning and the furnace should come on and heat, it does. It has a programmable thermostat and we set for 73 day and 67 night, When the night time low is 50 degrees, the house never cools down to 67 at night.

Do you have the old fashion mercury one that was previously installed there? Maybe it's a problem with the t-stat. Try installing a old one in it's place. If it shouldn't be calling for heat, fan, or recirculation, then the fan should not be blowing. That is easy enough to test. Disconnect the 24v line to t-stat (usually red)before bed. With out that connected, the t-stat can't call for heat/fan/cool. If the furnace blower still turns in the middle of the night then you have ghosts.

I think the ghost idea has merit. The Lux thermostat model mentioned in my above post is a 5 year old design and has no mercury.

Is it possible that the thermostat has a mode for the blower to come on every few hours, even if no heat is required in order to stabilize temperatures between rooms and confirm it isn't just mounted in a well Insulated part of the house?

No, it is a new problem on a thermostat that has been there for several years and a new replacement does the same thing. I think the problem is not in the thermostat because the new replacement does the same thing.