My problem is a little bit different then those I read about. My thermostat just started not to turn my fan on when the heat starts up, causing it to shut off. The only way my heat works now, if I manual turn the fan setting from AUTO to ON. Which causes my fan to run all day. Please help! It was 51 degrees this morning.

Sounds like you have a bad heat sequencer/fan control. Use the wiring diagram on the unknown brand furnace and track down this part. Replace or test with your meter then replace.

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Originally Posted by hvac1000

Sounds like you have a bad heat sequencer/fan control. Use the wiring diagram on the unknown brand furnace and track down this part. Replace or test with your meter then replace.

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What does this part look like. I think mine is black with a small toggle switch. Is this part right. If sso where could I get a replacment part. Thanks for getting back earlier.

Tell us more about your furnace.
Gas or electric
Brand
Brand model number.

Lennox G23Q2/3-75-4 serial #5896M25583

((My thermostat just started not to turn my fan on when the heat starts up))

What fan are you talking about? The little combustion air fan or the blower fan?

Blower Fan

Since the blower fan will not come on when the furnace is on in the automatic setting you have a problem with the fan control. I have no drawings for lennox but if you look at the wiring diagram on your unit it should show some kind of a fan control. At least you are not out of heat since you can turn the blower on and leave it run.