Hello, I have the wonderful Goodman GMP075-3 gas furnace with intermittent problems. I have read up on common problems but none fit my situation.

First, when the thermostat calls for heat the draft inducer kicks on for a few seconds then quits. The LED on the board flashes 3 times showing a draft fault. If I turn the thermostat off then back on everything works properly. It may then work for 3 or 4 cycles, some times more some times less, and then the same problem occurs. I cleaned the flame sensor, I pulled the rubber tube for the vent switch and tried to suck on it or blow on it when the thermostat was calling for heat and nothing happened though I could hear a click in the switch. I have a 3 year old digital round honeywell thermostat and replaced it with a new one that is an analog round dial by honeywell. This hasn't solved my problems. Now after the draft inducer comes on, the igniter will cycle 4 or 5 times or more before it fires if, it fires at all. I am at a loss for what is wrong. The only error code is 3 flashes. The draft is fine, I just installed a new flexible chimney liner, I removed the vent at the top of the furnace and can feel the draft drawing air. When the system is reset it works fine for a bit, maybe all day or only 1 cycle, then the draft inducer will kick on then shut off, or nothing will happen at all, the house will just get cold and I will never hear the draft inducer come on.

Should I start by replacing the pressure switch? I need to borrow a multimeter and test all the sensors.

Any help is appreciated.