ADH1992
New Member
Hello everyone, I started having what was originally an intermittent issue last winter that has developed into a persistent issue. Last winter, my thermostat would call for heat, and the flue fan would kick on, but the furnace would never actually fire up and produce heat. I'd flip the power switch off and back on and it would usually come back online immediately and resume normal function for a while (generally a few weeks before it would happen again). At the beginning of fall this year, I kicked it on to make sure it was going to work, and it had the same issue, except now it's constant. The thermostat calls, the flue fan runs, but the burners don't come on.
This is where my troubleshooting begins. With everything hooked up like it has been, when the thermostat calls for heat, the flue fan comes on, and the inducer fan spins at about half speed in the clockwise direction. The furnace stays in this state indefinitely while the control board flashes a "pressure switch stuck in open or closed position". If I unplug either of the wires or the vacuum hose from the pressure switch, the inducer slows down, changes direction and spins full speed in the counterclockwise (correct direction) and the furnace starts up like it should. I plug the line back in, and it runs normally until it satisfies the thermostat and then shuts off as normal. On the next heating cycle, the whole process starts again. It'll run without firing up until I unhook and reconnect the pressure switch.
As far as I can tell, the pressure switch and flue are working correctly. There are no blockages between the furnace and the exterior of the house through the flue pipes. Changing pre-purge time didn't affect functionality. To someone with zero HVAC experience, it seems to me like the pressure switch may be closing too quickly upon firing up and the furnace thinks it's in an always closed condition, thus not continuing the startup sequence any farther.
Thanks for any suggestions.
The furnace is a Ducane MPGA125858
This is where my troubleshooting begins. With everything hooked up like it has been, when the thermostat calls for heat, the flue fan comes on, and the inducer fan spins at about half speed in the clockwise direction. The furnace stays in this state indefinitely while the control board flashes a "pressure switch stuck in open or closed position". If I unplug either of the wires or the vacuum hose from the pressure switch, the inducer slows down, changes direction and spins full speed in the counterclockwise (correct direction) and the furnace starts up like it should. I plug the line back in, and it runs normally until it satisfies the thermostat and then shuts off as normal. On the next heating cycle, the whole process starts again. It'll run without firing up until I unhook and reconnect the pressure switch.
As far as I can tell, the pressure switch and flue are working correctly. There are no blockages between the furnace and the exterior of the house through the flue pipes. Changing pre-purge time didn't affect functionality. To someone with zero HVAC experience, it seems to me like the pressure switch may be closing too quickly upon firing up and the furnace thinks it's in an always closed condition, thus not continuing the startup sequence any farther.
Thanks for any suggestions.
The furnace is a Ducane MPGA125858
