Heat call: inducer does not start but cooling and fan work

What is going on

This is the one where the thermostat is calling for heat and the furnace just sits there, but the cooling and the fan work fine. That tells you the 24 volts and the blower side are fine, so the problem is in the heat sequence ahead of the inducer. Most of the time a limit is open, so start with the LED code. The control will tell you a lot. On the SureLight board LED1 slow flash with LED2 on points at a limit being open. Check that before you start pulling wires.

Likely causes

• Primary or secondary limit open
• Wiring or connection problem at the limit switch(es)
• Wiring problem at the combustion air inducer
• Inducer failed
• Prove switch stuck closed

Check in this order

1. Turn off power at the disconnect before touching wiring or components
2. Check the LED pattern first (LED1 SLOW / LED2 ON means limit open)
3. Check limit continuity and the airflow and filter
4. Check the inducer wiring and look for 120 V at the inducer
5. With the inducer off, confirm the prove switch is open. Replace it if stuck closed
6. If the limit is open with a dirty filter, fix the airflow, do not simply replace parts
7. Replace only what tests bad, and verify a complete heat cycle

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