Combustion blower motor runs all the time - Heating & Cooling

Check the combustion chamber blower motor. When the motor bearings die, this can happen.

Guessing. Combustion blower motors often have power to the motor wires or leads , and a pair of signal wires or leads as a sensor for motor operation. This sensor feature is so the burner is not activated if the combustion blower motor does not work
The sensor integrated in the motor may be a centrifugal switch or a hall switch / sensor that connects to the combustion control board as a safety.
Replace the motor, along with the sensor, if either motor or sensor fails.

Is there noise when the inducer motor comes on? The small motor that comes on first. It sucks the co out of the combustion chamber. It comes on first. Then the burner lights then the blower comes on. And the noise continues while it's running and doesn't stop till the blower stops? Is that correct? But it's not the blower wheel? Could it be out of balance and hitting the blower shroud?

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If you bypass tstat, meaning hot wired blower, does the blower cycle on and off by touching and removing red with fan?? If yes than obvious problem in tstat. I was leaning towards a bad relay but if you can make it work by passing tstat, there's you problem.

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You are going to need a service man. A magnehelic gauge is needed to properly diagnose a pressure switch issue. Could be a blocked or restricted flue, a defective induced draft motor, cracked heat exchanger, restricted secondary heat exchanger, ect. ect.

EE8 is the code for combustion blower failure. I'm not sure which fan you checked. You can't see the combustion blower fan. It is inside the black plastic cover on the back side of the heater near the bottom. You can see the motor for it from inside the heater. The blower has a sensor to determine fan speed to control the amount of airflow to the burner. There could be a problem with the sensor. When you turn the heater on the first thing you should hear is the combustion blower start up and run. On the smaller heaters they are very quiet and sometimes hard to hear. Start the heater and see if the blower starts. If it doesn't remove the front cover and locate the blower motor so you can check the wires going to it. I have seen wires that mice have chewed off. Otherwise you may need a need blower motor. If it is running then the sensor is possibly bad and you would also need a new blower motor. Also make sure the exhaust pipe isn't blocked since you say the house smells like diesel. Let me know what you find. [email protected]

Usually when the furnace blower motor runs all the time
The limit switch or rollout switch is usually open or bad.
The furnace board is seeing that one of those switches is open, so it brings the blower on to try to get the heat out of the combustion chamber area, so the switch will close. But if the switch is bad and won’t close, the furnace board will keep the blower running continuously.

Usually when the furnace blower motor runs all the time
The limit switch or rollout switch is usually open or bad.
The furnace board is seeing that one of those switches is open, so it brings the blower on to try to get the heat out of the combustion chamber area, so the switch will close. But if the switch is bad and won’t close, the furnace board will keep the blower running continuously.

The whole assembly must be replaced.

The sequence of operation is -

Combustion fan purges the heat exchanger. A pressure switch verifies combustion air fan is running. Usually a 30-45 second purge before the hot surface ignitor glows, or the spark ignition starts.

Gas valve opens after 10-15 seconds and main burners light. Control board monitors for flame and shuts gas valve after 2-3 seconds if main burner does not light.

If burner does not light, some boards repeat this for 3 tries, then locks out and is reset by cycling power.

Air blower comes on after another 30-45 seconds after main burner ignition.

Times may vary based on the specific controller board. A flow chart and timing sequence should be located somewhere on the unit, usually in the fan compartment.