After 10 - 20 seconds, I'm guessing the controller again calls for heat, as the ignitor turns on, flame ignites across all burners, the blower motor comes on, and normal heating resumes. During the event onset, there is rapid voltage change at the Pressure Switch leads. The control light changes from Fast Flash to 3 Flash. Then the solenoid on the valve will active 3 to 10 times in rapid succession (e.g., 1 to 2 clicks per second) and the flame is extinguished The draft inducer continues to run while the blower motor stops. My ~20 year old Trane XE80 starts up and runs fine for 3 - 10 minutes. Also replaced the limit switch with a new one. I thought there are issues with the blocked vent (S62) and flame rollout (S47) switches, so I bypassed them with a jumper but the issue still persists. I noticed on colder days takes even longer. This takes longer than usual, obviously for the on/off flame cycle. This cycle repeats itself until the temperature in the house reaches the one set on the thermostat. After about 2 minutes, the damper opens and the flame ignites again. The heat starts off fine, the flame ignites, the fan blows fine but after 3 minutes the damper shuts off (flame is off) while the fan is still blowing. So, a strange behavior on our Lennox WhisperHeat heater (model: G20Q3/4E-100-5) for the past week or so.
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