Blower fan keeps running but burners shut off during heat call between 3-4 mints of initial start up.
Replaced the filter which was fully blocked but problem is consistent. Any suggestion
Do you see a LED light, on the furnace control board, flashing a code? Have you tried cleaning the flame sensor?
Yes i have cleaned flame sensor. Burner come on for 4 mint when first start and than blower fan keeps running, thermostat in on auto. Can this be faulty limit switch?
Furnace model: c9mpd075f12c2
LED Code: 3 blinks
It's a low pressure switch lockout code, according to the ICP C9MPD manual (https://www.questargas.com/ForEmployees/qgcOperationsTraining/Furnaces/Day&Night_N9MP%20C9MP%20H9MP%20T9MP.pdf).
Check that your venting is clear and sloped properly, and check the P-trap and drain line are clear.
If those things checkout use a multi meter and manometer to verify if you might have a faulty control board or pressure switch.