HVACopediaLennox · Furnace troubleshooting
Furnace will not run (no heat) - Lennox SL297NV
What is going on
Basic checks from the manual when the SL297UHNV does not operate.
Likely causes
- No heat call
- Access panel off
- Power off
- Dirty filter
- Gas off
- Ignition lockout (Watchguard)
Check in this order
- Confirm the thermostat is calling for heat.
- Make sure access panels are secure.
- Check main disconnect, fuses and breakers.
- Check the filter; a plugged filter will trip the limit (E250).
- Confirm gas is on at the meter and both the main and internal manual valves are open.
- Check the 7-segment display for an E-code; if the unit is in Watchguard lockout (auto-retry after 60 minutes), move the thermostat from Heat to Off and back to Heat to restart, and inspect for blockages if it locks out again.
Applies to: SL297UHNV
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Source: Lennox SL297UHNV Installation Instructions 507760-02 (02/2018), Failure To Operate and Heating Sequence, p.49. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.