Bryant Plus 90 398AAZ Not Firing

[Ltvscout]

Went to use the furnace for the first time this fall last night. Turned on the thermostat and heard the inducer motor spin up. I walked away but then noticed 5 mins later that the furnace wasn't running. Checked to make sure the thermostat was calling for heat. Went downstairs, flipped of the power, turned it back on and the inducer motor spun up again. But, after 20-25 seconds it shut off with no pilot start. I tried this a few times, on/off with the power switch, and it finally took. It worked all of last night. This morning, no heat again. No matter what I tried I can't get it to fire anymore. The inducer motor will run for 20-25 seconds and then just shuts off.

What should I look for to troubleshoot?

Thank you for any help you can offer.

Scott

[HayZee518]

heater

check the roll out switches

[Ltvscout]

check the roll out switches

??? The only switches I'm aware of are the blower door safety switch and the pressure switch.

All the rest of the switching I can see is done by relays.

[Ltvscout]

check the roll out switches

Sorry, being that I'm in IT and not HVAC I was not aware of what a rollout switch was. After googling it I see that my old furnace (circa 1990) doesn't have a rollout switch, but does have a limit switch. I'm assuming that is an open/close type of switch and I can test it by using an ohmmeter across the two terminals to see if the switch is open or closed?

Scott

[Brian_Martin_Parma_Air]

Bryant Plus 90 Furnace Diagnosis

I see you and trying to repair you own furnace. I don't blame you, furnace repair techs are usually pretty expensive. Here are 4 things that might be going on in your situation. 1. You might have a bad connection between the thermostat and the central control board. Unhook everything and hook it back up. Look for corrosion and clean the contacts. 2. You could have a faulty circuit board. Hard for a do it yourselfer to diagnose. 3. Could be a bad relay. 4. Usually, it's an Ignition control module issue or the igniter itself. The igniter would be the cheapest to swap out and sometimes fixes this problem. The ignition control module can get expensive. See if there is a light on the ignition control module that turns red or blinks. If it's not green, there is a problem. Brian Martin.

[Ltvscout]

Thanks, Brian. It ended up being the ignitor lockout control box. All is well again. My buddy who does HVAC on the side had a used one for me.