Lennox Furnace: Furnace will not run – Lennox SL280UHV checklist
Furnace will not run - Lennox SL280UHV checklist on a Lennox furnace: SL280UHV / SL280UHNV furnace does not start on a heat call; basic checks from the installation manual before deeper diagnosis.
Applies to: Lennox SL280UHV (SL280UH070V36A, 090V36B, 090V48B, 090V60C, 110V60C, 135V60D) and SL280UHNV (SL280UH060NV36A, 080NV48B, 080NV60C, 100NV60C) 80% two-stage variable-speed communicating furnaces
Common causes of furnace will not run - lennox sl280uhv checklist
- No thermostat call
- Panels off (door interlock open)
- Power off, blown fuse or tripped breaker (incl. 3 A 24 V breaker)
- Gas off
- Dirty filter tripping limit
- Lockout
- Pressure switch open (blocked flue)
- Flame rollout switch tripped
How to fix furnace will not run - lennox sl280uhv checklist: step by step
- Confirm the thermostat is calling for heat.
- Make sure the access panels are on (door interlock switch).
- Check the main disconnect, fuses/breakers, and the 24 V circuit breaker on the control box (3 A, push to reset).
- Make sure gas is on at the meter, the main manual shut-off and the internal gas valve switch.
- Check the filter - a dirty filter makes the limit shut the unit off.
- Check the 7-segment display for an error code (hold the button for 'E' to recall the last 10 codes). Watchguard lockout resets after one hour.
- Check the pressure switches and flue/vent outlet for blockage.
- WARNING: If a flame rollout switch has tripped, find the cause (combustion air, blocked vent) before resetting it.
If the unit shows an error code, look it up: Lennox Furnace codes
Models
Lennox EL195UHNE
EL195UH040NE36BEL195UH060NE36BEL195UH080NE48CEL195UH100NE60C
EL296UHV
EL296UH045XV36BEL296UH070XV36BEL296UH090XV36CEL296UH090XV48CEL296UH090XV60CEL296UH110XV48CEL296UH110XV60CEL296UH135XV60D
Lennox ML180UHE
ML180UH045E36AKML180UH045XE36AKML180UH070E36AKML180UH070E36BKML180UH070XE36AKML180UH070XE36BKML180UH090E48BKML180UH090E60CKML180UH090XE48BKML180UH110E60CKML180UH110XE60CKML180UH135E60DK
Lennox SL280UHV
SL280UH060NV36ASL280UH070V36ASL280UH080NV48BSL280UH080NV60CSL280UH090V36BSL280UH090V48BSL280UH090V60CSL280UH100NV60CSL280UH110V60CSL280UH135V60D
Lennox SL297NV
SL297UH040NV36BSL297UH060NV36BSL297UH080NV48CSL297UH080NV60C
Source: Lennox SL280UHV Installation Instructions 508245-01 (04/2024), Failure To Operate, p.44; Lennox SL280UHNV Unit Information Corp 1601-L8 (rev 04/2024), Circuit Breaker CB8, p.11. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.