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Lennox · technician tips

Lennox service menus, test modes and resets

6 tips for air conditioner, furnace, heat pump: access codes, button combinations, test modes and the resets you need at the appliance.

Jump to: Button combinations (1) · Service & test modes (3) · Reset & cancel (1) · Commissioning (1)

Button combinations

Key presses that open menus, show readouts or switch modes.

Recall or clear the last 10 error codes (red LED button)

Furnace · Lennox EL195UHNE

A button next to the red LED replays the stored error codes, newest first; holding it clears them.

  1. Press and release the button to start recall (newest code first).
  2. Watch the red LED flash each code, with a 3 second pause between codes.
  3. To clear the stored codes, press and hold the button for more than 5 seconds.

Applies to: EL195UHNE furnaces with ignition control 103217-03 or 107163-01 (red LED)

Source: Lennox EL195UHNE Unit Information Corp 1801-L1 (rev 04/2024), Table 4 (103217-03) / Table 5 (107163-01) diagnostic codes, p.8-10. Written in our own words; check the manual for your exact model.

Service & test modes

Forced fan, low and high fire, test and diagnostic modes, error history and live data.

Simulate a refrigerant leak with the RDS Test button

Air conditioner · Lennox EL16KC1

After the 5-minute purge, pressing Test during a call makes the board act as if a leak was found, which checks wiring and response.

  1. Restore power and wait for the 5-minute purge to finish.
  2. Cooling check: start a cooling call at the thermostat, press Test on the RDS board, and confirm the LED flashes blue, the blower runs and the outdoor compressor stops.
  3. Press Test again to end the simulated leak.
  4. Heating check (gas furnace): start a heat call, press Test, and confirm the blue flashing LED, blower on, burners off and compressor off. Press Test again to end it.

Applies to: Lennox EL16KC1 A/C with RDS blower control board 27A02 (R-454B)

Source: Lennox EL16KC1 (Elite A-C, R-454B) Installation Instructions 100121 (01-2025), Start-Up Test Procedure (RDS Blower Control Board), printed p.35-36. Written in our own words; check the manual for your exact model.

Test or reset the Low GWP refrigerant detection board (Test button)

Furnace · Lennox ML180UHE

A short press in Normal mode simulates a leak response (E164 for about a minute); in Leak Detected or Fault mode it resets the board after the problem is fixed; while initializing it skips the rest of the pre-purge.

  1. To test after installation: restore power and wait for the initializing purge to finish.
  2. Start a cooling or heating call and press the Test button; the blower should start, the compressor should stop (and the burners on a heat call).
  3. Press Test again to end the simulated leak.
  4. After a real leak or fault is resolved, press Test to bring the board back to Normal.

Applies to: Lennox ML180UHEK furnaces with Low GWP refrigerant detection control board

Source: Lennox ML180UHEK 100166, Furnace Control Board Low GWP Modes of Operation and LGWP Test Button Functionality (Tables 18-19), printed p.34-35. Written in our own words; check the manual for your exact model.

Use the defrost control TEST pins to clear lockouts or force defrost

Heat pump · Lennox EL16KP1, Lennox ML14KP1

A jumper on the TEST pins (P1) clears short cycle and five-strike lockouts and forces the unit into and out of defrost; the 30 s defrost off-delay does not work while it is fitted.

  1. Place the jumper on the TEST pins of P1.
  2. Use it to clear the lockout or to cycle the unit in or out of defrost.
  3. After testing, move the jumper back across the desired defrost termination temperature pins (factory setting 50 F).

Applies to: Lennox EL16KP1 (Elite) and ML14KP1 (Merit) R-454B heat pumps, sizes -018 to -060, demand defrost control A108 (CMC1)

Source: Lennox EL16KP1 Unit Information 100195 / ML14KP1 Unit Information 100108, Defrost Control Connections, Test Pins (P1) Function, p.31. Written in our own words; check the manual for your exact model.

Reset & cancel

Clearing lockouts, service reminders and fault history; skipping purge or de-air programs.

Clear stored error codes in the error recall menu

Furnace · EL296UHV, Lennox SL280UHV, Lennox SL280UHNV, Lennox SL297NV

The lowercase c in the error recall menu erases all stored codes; it must be confirmed while it flashes.

  1. Enter error recall by holding the button until E shows, then release.
  2. Scroll the recall menu until c shows (it changes about every 5 seconds).
  3. Press the button again while c is still flashing to delete all stored codes.
  4. Exit by holding the button until three bars show.

Applies to: Lennox EL296UHV, SL280UHV/SL280UHNV, SL297UHNV and ML180UHEK furnaces with 7-segment integrated control

Source: Lennox SL297UHNV Installation 507760-02 (02-2018), Integrated Control Diagnostic Modes, printed p.54; also SL280UHV 508245-01 p.51, SL280UHNV 1601-L8 Table 4, ML180UHEK 100166 p.12. Written in our own words; check the manual for your exact model.

Commissioning

Start-up and set-up steps that are easy to miss.

Program the unit size code on a replacement furnace control

Furnace · EL296UHV

A replacement control needs the furnace size code stored; three bars then E203 at power-up means no valid code.

  1. Thermostat OFF and control idle.
  2. Hold the button until a solid P shows, then release.
  3. Hold the button again and release when the right size code shows.
  4. Within 10 s hold the button for 5 s to store it.
  5. Cycle 24 V power to confirm the code was saved.

Applies to: All EL296UHV models: EL296UH045XV36B, 070XV36B, 090XV36C, 090XV48C, 090XV60C, 110XV48C, 110XV60C, 135XV60D

Source: Lennox EL296UHV(X) Unit Information, Corp 1125-L5 (rev. 03/2022), IX Program Unit Capacity Size Modes, p.110 (printed p.109). Written in our own words; check the manual for your exact model.

Related

Lennox error codes

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For licensed technicians. Installer menus, test modes and access codes change settings that affect safety; only use them if you are trained on the appliance and understand the result. Gas, electrical and refrigerant work must be done by a qualified, licensed person, and the manufacturer’s manual for the exact model and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.