Lennox Error Code E390: Low GWP relay stuck (Furnace)
Lennox error code E390 on a furnace means: Low GWP relay stuck. It is also called Lennox diagnostic code E390.
Homeowner? What Lennox code E390 means for you
Call a technician Your furnace is reporting: Low GWP relay stuck. The furnace has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
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 E390 mean?
The Low GWP relay on the furnace control is not working correctly. The control may need replacing. Clears when the relay operates normally.
Applies to: ML180UHEK (R-454B era) single-stage 80% furnaces with integrated control 107792-XX (ML180UH045/070/090/110/135, incl. low-NOx X models)
Common causes of Lennox code E390
- Failed Low GWP relay on the integrated control
Lennox models that use code E390
ML180UH045E36AKML180UH045XE36AKML180UH070E36AKML180UH070E36BKML180UH070XE36AKML180UH070XE36BKML180UH090E48BKML180UH090E60CKML180UH090XE48BKML180UH110E60CKML180UH110XE60CKML180UH135E60DK
Other Lennox Furnace codes
All Lennox Furnace error codes →
Lennox code E390: homeowner questions
What does Lennox code E390 mean?
Low GWP relay stuck. The Low GWP relay on the furnace control is not working correctly. The control may need replacing. Clears when the relay operates normally.
Is it safe to keep using my furnace with code E390?
It depends on the cause. The furnace has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
Can I reset Lennox code E390 myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code E390 comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code E390 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
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Source: Lennox ML180UHEK Unit Information 100161/100166, Table 6 Integrated Diagnostic Codes, p.15. 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.