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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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My Lennox pulse 21 starts up upon thermostat demand. The

Customer Question

My Lennox pulse 21 starts up upon thermostat demand. The heat continues for about two minutes the the igniter begins to struggle and shuts off before desired room temperature is reached. After a few minutes the igniter turns back on until room temperature is reached. What causes this?
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: I have a new air filter, I replaced the flapper. The thermostat does not shut the igniter off because the room temp is not reached.
JA: Do you plan on doing the work yourself?
Customer: If it is simple. Could it be a plugged condensate trap? I hear water drips in the main pipe?
JA: Anything else we should know to help you best?
Customer: Not sure
Submitted: 9 months ago.
Category: HVAC
Expert:  BillyHvac replied 9 months ago.


My name is ***** ***** I will do my best to assist you. I am looking over your question now and will respond shortly.

Expert:  BillyHvac replied 9 months ago.

when was the last time the spark plug and flapper membrane were replaced?

Expert:  BillyHvac replied 9 months ago.

These use a spark plug like a car.

They have long been discontinued and parts are getting a bit harder to get and more expensive.

This furnace is different than any other unit as it requires "tuneups" like a car does.

Here is a tuneup kit parts list

Let me know last tuneup date and we can go from there