Lennox Error Code E403: LSOM – compressor short cycling (Furnace)
Lennox error code E403 on a furnace means: LSOM - compressor short cycling. It is also called Lennox diagnostic code E403.
Homeowner? What Lennox code E403 means for you
Check, then call Your furnace is reporting: LSOM - compressor short cycling. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Safe things you can check yourself
- Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
- Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
- Make sure the furnace front door or panel is closed properly; many furnaces will not run with the door switch open.
- Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
- Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
- Check that the gas valve next to the furnace is open (handle in line with the pipe). Do not force it.
- Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.
Call (647) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Lennox error code E403 mean?
Compressor runs less than 3 minutes to satisfy demand (table title says less than 4 minutes). Note: the manual's text for this code is inconsistent; verify on the unit.
Applies to: EL296UHV(X) series furnaces with integrated control 103130-XX only
Common causes of Lennox code E403
- Pressure trips
- Thermostat cycling
Lennox models that use code E403
Show all 22 models
EL296UH045XV36BEL296UH070XV36BEL296UH090XV36CEL296UH090XV48CEL296UH090XV60CEL296UH110XV48CEL296UH110XV60CEL296UH135XV60DSL280UH060NV36ASL280UH070V36ASL280UH080NV48BSL280UH080NV60CSL280UH090V36BSL280UH090V48BSL280UH090V60CSL280UH100NV60CSL280UH110V60CSL280UH135V60DSL297UH040NV36BSL297UH060NV36BSL297UH080NV48CSL297UH080NV60C
Other Lennox Furnace codes
All Lennox Furnace error codes →
Lennox code E403: homeowner questions
What does Lennox code E403 mean?
LSOM - compressor short cycling. Compressor runs less than 3 minutes to satisfy demand (table title says less than 4 minutes). Note: the manual's text for this code is inconsistent; verify on the unit.
Is it safe to keep using my furnace with code E403?
It depends on the cause. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Can I reset Lennox code E403 myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code E403 comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code E403 near me?
Aurora Star Tech Inc. repairs Lennox furnaces in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: Furnace Not Turning On: What to Check · Furnace Blinking Light: What the Flash Codes Mean
Troubleshooting guides
- Blowing cold air All brands · Furnace
- No heat All brands · Furnace
- Short cycling All brands · Furnace
- Blower motor does not run - Lennox SL280UHV ECM checks Lennox · Furnace
- Display shows two horizontal bars (soft disable) - Lennox SL297NV Lennox · Furnace
- Furnace will not run (no heat) - Lennox EL195UHNE Lennox · Furnace
- Furnace will not run (no heat) - Lennox SL297NV Lennox · Furnace
- Furnace will not run - Lennox SL280UHV checklist Lennox · Furnace
- Indoor blower does not run - Lennox EL195UHNE Lennox · Furnace
- Indoor blower does not run - Lennox ML180UHE Lennox · Furnace
- Poor ignition or combustion resonance - Lennox EL195UHNE Lennox · Furnace
- Poor ignition or loud combustion resonance - Lennox SL280UHNV Lennox · Furnace
- Two horizontal lines on display (soft disable) - Lennox communicating Lennox · Furnace
Source: Lennox EL296UHV(X) Unit Information / Service Literature, Table 5 Ignition Control 103130-XX Diagnostic Codes, p.37. 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.