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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Got a gibson high efficency short cycling right after the

Customer Question

hi, got a gibson high efficency short cycling right after the inducer motor steps down shortly after the fan comes on.... about 45 secs into the burn.
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: a few days...
JA: Do you plan on doing the work yourself?
Customer: I have an epa class II license.
JA: Anything else we should know to help you best?
Customer: furnace is about 6 years old..
JA: Did you check the furnace's filters?
Customer: yes, even removed them, no change
Submitted: 8 months ago.
Category: HVAC
Expert:  Phil replied 8 months ago.

Hello, I need to get clear on this sequence. Please tell me if I am accurate or not, and in great detail what the furnace is doing.

1.Thermostat calls for heat

2. Inducer fan comes on.

3. two seconds later you hear a faint click as the pressure switch closes

4. Inducer blower keeps running for 30 to 50 seconds, then the control board closes 2 relays, one for the igniter and one for the gas valve.

You can hear those two faint clicks.

5 Burners ignite.

6. about 30 seconds later the main blower (not the inducer fan which is already running) comes on.

7. The burners stay on until the house is warm...OR the burner goes off because the flame sensor is not sending the flames... that can happen anywhere between 4 to 10 seconds after the burner lights as a rule...

In that case, the furnace will try to fire 3 to 5 more times, same cycle... if all 5 times fail, then it will lock out the controls so that you must do a 'soft reset' by cycling the thermostat OFF then back ON.

Please comment in detail, we can go from there