Inducer fan runs but furnace does not light. no flashing lights

Jimbo, it sounds like you are aware of the operational sequence to suggest using a voltmeter to check the actual wires going TO the combustion air fan...if there is no voltage from the board, the board is bad. Just make sure one of the high temp limits are not open... one may be in the blower compartment on some and one will be near the top of the vestibule and a roll out switch should be near the burners. They should all be wired in series.

Always check the manual reset safty switches as the first step in troubleshooting.

possibly a board issue does inducer shut off when no call for heat

If the inducer runs for a short time and shuts off and the main blower comes on and runs it could be a high limit switch or a roll out switch.it could also be a pressure switch that is stuck in the closed position. Most new furnaces have to read the pressure switch in the open position and then the closed position after the inducer fan starts. . Hope this helps.

this indicates fault 33, on inside of access panel will tell you faulty switch. i believe off top of my head is pressure switch open, this a safety switch to verify that inducer fan is working, several things besides a failed part can cuase this, there is a rubber hose going from the inducer fan houseing to the safety pressure switch, remove hose from fan housing and run a small stick ,wire or torch tip cleaner, down the acces port, calcium builds up inside the port and blocks the sampling of pressure, reassemble and try it, if this works add it to yearly maintenance could need new switch or inducer fan motor, these need to be replaced by a tech, also birds can block flue pipe

You are correct. If the inducer motor is warm, but not running, it has seized up. If you replace this yourself, I also suggest that when you replace the inducer fan, check to make sure the secondary heat exchanger isn't clogged, or the condensate drain(s). If you have an HVAC contractor replace it, he should do this for you. It shouldn't run more than $350, to have it replaced and he can check for clogs (The price I'm quoting is for standard hours).

You can check this yourself by running the inducer fan without it being attached to the furnace, then attaching it to the furnace. If you notice a significant reduction in airflow, then you have a clogged secondary heat exchanger. I've run across this situation before on this particular model. The owner recenly replaced the inducer motor, but couldn't figure out why he was still having problems. I suspect the clogged heat exchanger contributed to the inducer motor to failing previously, and feel It would definitely be worth checking while you have the fan removed to help eliminate any future problems that could result from this, including heat exchanger failure. The manufacturer of this unit actually recommends you clean the secondary heat exchanger every year, but this is overkill if your furnace was installed and set up properly. I'd recommend doing it every 10 years and you're at that mark now. Instructions on how to do this are in the manual for this unit if you have it. Otherwise, e-mail me at [email protected] and I can send you a copy.

Finally, check the limit and flame roll out switches after replacing, as they could have tripped when the motor failed.

Have some one hold the bottom door safety switch, turn furnace on wait until heating fan relay clicks, and check at terminal (Heat) & terminal (neutral or where all the white wires are located on the control board) for 115 volts to 120 volts. If voltage is present replace blower motor, if voltage drops out while running then replace control board.Turn power off to furnace, open bottom door and feel blower motor with hand, if motor is real hot replace motor. you can not oil this type of motor, it has to be replaced along with the compacitor. Good luck.

That control board is several hundred dollars. If I may make a suggestion, take a jumper and when the inducer fan starts, jump out the pressure switch. If it starts, it's not the board but a bad switch, hose or blocked exhaust vent.

When a furnace is replaced with a newer style unit like yours with an inducer motor, they sometimes use the old vent pipe. These old style vent pipes are transite (light weight cement), the moisture created from your furnace exhaust is caught on the cool transite surface and runs back down into the blower blades or wheel bringing a white mineral deposit with it which causes your problem. The vent should nave been replaced with the heater using a metal vent material. You will need to replace your inducer motor assembly and vent pipe to prevent a recurrence.

try checking the pressure sensing switch,it has a tube that should run somewhere close to the inducer fan.sometimes this hose fills with liquids,and makes the units act funny.I don't know if you have a condensing unit or what.the furnace wont try to light if it cant tell the inducer motor is running.any induced draft unit will work this way.you can also do a temp. bypass of the pressure switch to make sure the contacts on it are closing just be sure your inducer fan is running,and you cant leave it like that its just a test.that is a safety feature you really need.