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It would be very helpful if you could provide the type of heating system (natural gas, propane, fuel oil, or electric) and the make and model number.
I recently repaired a natural gas system with a similar problem. The control circuit board had diagnostic lights flashing a code for five flame sensor failures in a cycle. The furnace would ignite a flame, then shut it off after a couple of seconds, then repeat until the fifth try. The flame sensor electrode was coated with solid material from contaminants in the gas. I polished it with Scotch-Brite (TM) and got it to work properly. What is different in this case is that the blower would also not run unless it was set to blow continuously.
Do you have the model number? There is a problem with either the blower motor sensor or the ignitor. When the furnace get a signal for heat, the blower motor comes on and then the ignitor. If either one of those fail then it stops, waits and tries again. When the tech was there, if he did not replace any parts then he did not do his job. You can call them back out because the issue was not resolved or you can post the model number for us.
Sounds like the automatic fan control is not working it cuts in on temp rise . It may be dirty on the back of it as you said you had a smell of dust burn
This just sounds like a couple of problems. First, your blower is designed to only turn on once the heat exchanger heats up, so the flame will be on for a minute or two before the blower starts. it sounds like your blower is cooling down the heat exchanger too fast and causing it to shut off so it can warm up again...check blower speed for heat, it should be the lowest speed (black wire). Blue=medium speed, red= high speed. second problem could be your flame sensor rod is calcified, you just need to locate this and clean it off with some fine sand paper.it is located in the flames near the burners. Also change your filters, for proper air flow through your heat exchanger.
The fan limiting switch is acting up. It should stay running until lower temp is reached. It will cycle until the temp stays below or at the low setting. Limit switches are adjustable.
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