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I have an approx 20-year old Tempstar (model # NUGK125DK08, manufactured by 'Inter-City Products') 90% eff gas-fired furnace. Yesterday morning we noticed it was blowing only cold air. I opened it up and noticed a faint burning smell and poked around and noticed the inducer motor was hot and was not running when the furnace was switched on. I got the part today and replaced the inducer unit, which is running fine now when the furnace is switched on, but there is no ignition. What to check next?

Edit: @Mazura was right - it was the pressure switch. Note- in my previous comments, I mistakenly thought the heat switch mounted right on the inducer assembly housing was a pressure switch.

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  • Check voltage to the igniter next.
    – A. I. Breveleri
    Commented Apr 6, 2018 at 23:08
  • Checked any of your limit switches? Listed for the gas valves to open or close, watch for ignition spark or glow.
    – Jeff Cates
    Commented Apr 7, 2018 at 0:29
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    What is the current ignition sequence? If there's a limit that's not in the correct position (opened/closed), if could just be causing the inducer to run continuously (purging).
    – Tester101
    Commented Apr 7, 2018 at 1:19
  • Do you have the model number?
    – Tester101
    Commented Apr 7, 2018 at 3:04
  • Yes; edited to put the model up there.
    – hotkarl
    Commented Apr 7, 2018 at 5:04

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Pressure switch on the inducer has to be satisfied before it will light the ignitor. If it can never verify that the inducer is blowing, it might run it forever and burn it out.

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  • Agreed. Check to make sure the pressure switch is closing as it should, and that all other switches are making/breaking as they should.
    – Tester101
    Commented Apr 7, 2018 at 1:21
  • Definitely check everything else. I didn't look up this particular unit, but "just blowing cold" is indicative of a plenum over heat sensor gone bad (or doing it's job). And a continuously running inducer is the 'error code' for units that are old enough.
    – Mazura
    Commented Apr 7, 2018 at 1:25
  • Thank you for the help- I turned it on with 1)one wire disconnected from the pressure switch- blower ran, inducer did not; 2)both wires disconnected from pressure switch and connected directly to each other- both blower and inducer ran. In both cases, there was no heating up of ignitor and no gas smell.
    – hotkarl
    Commented Apr 7, 2018 at 2:33
  • My last comment was referring to the pressure switch mounted directly on the inducer fan blade housing, btw. Next I'll check the fan and limit switch - sorry I am a novice and this is a slow process for me- I don't seem to have a heat sensor or a thermocouple but above I do have a honeywell fan limit switch - does this seem like a good thing to focus on next?
    – hotkarl
    Commented Apr 7, 2018 at 3:13
  • @hotkarl - continue to check sensors but add the model number to your post. If it has a HSI see if it's cracked or broken. If it has spark ignition, I'm only familiar with that on hot WHs, which usually means new control board/gas valve.
    – Mazura
    Commented Apr 7, 2018 at 3:27

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