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Tell me what the pattern of the flash is For example 2 flash pause or three flash pause, etc
OK turn high voltage power off to furnace at switch or breaker.THis will reset board.Then back on and call for heat and tell me what happens and if we get same 3 flash code.
OK the 3 flash code is an ignition failure issue but we have to find why it failed. Do you have a volt meter to see if we are getting power to the exhaust vent fan?
OK here is the proper sequence we should have.
Thermostat calls for heat the combustion motor starts immediately
Combustion motor pulls a vacuum on the pressure switch closing it
30 seconds later igniter is energized for 15 seconds
Gas valve opens and burner lights
Flame sensor verifies we have flame.If no flame in 6 seconds, burners shut back off
Sequence will try 2 more times.If no flame sensed lockout occurs.
Ask where in that sequence it seems to be failing
Our first step is going to be to get a volt meter an check the 120 volts to that inducer fan and see if we get and keep 120v to that motor and verify if it actually comes on and if it stopping with voltage still to it.If fan is stopping and we still have power, the motor could be bad.
I am attaching pic showing where we should be getting 120v to combustion motor.
Also here is a link t a manual on the furnace.
Sequence of operation is on page 19
Some troubleshooting steps on page 23
Wiring diagram on page 32
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