Lennox Error Code E442: Compressor top cap switch strikes lockout (Heat Pump)

Updated October 13, 2026 · by Aurora Star Tech Inc.

Lennox error code E442 on a heat pump means: Compressor top cap switch strikes lockout. It is also called Lennox diagnostic code E442.

High severityHeat Pump

Homeowner? What Lennox code E442 means for you

Call a technician Your heat pump is reporting: Compressor top cap switch strikes lockout. The heat pump 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.
Check both breakers and the outdoor disconnect box beside the outdoor unit; all should be ON.
Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
In winter, keep snow and ice off and away from the outdoor unit. A short defrost cycle with steam is normal.
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) 657-2977 Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does Lennox error code E442 mean?

Compressor thermal protection opened five times within one hour; outdoor unit locked out. S30/S40 thermostat alert code 442 (shown as E442 on the unit control display).

Applies to: Lennox communicating heat pumps incl. variable-capacity inverter units in S30/S40 smart thermostat systems

Common causes of Lennox code E442

Compressor overheating (charge, airflow, TXV)

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

Lennox models that use code E442

EL16KP1-018 EL16KP1-024 EL16KP1-030 EL16KP1-036 EL16KP1-042 EL16KP1-048 EL16KP1-060 ML14KP1-018 ML14KP1-024 ML14KP1-030 ML14KP1-036 ML14KP1-042 ML14KP1-048 ML14KP1-060

Other Lennox Heat Pump codes

Code	Meaning
E435	Inverter EEPROM checksum fault (inverter code 60)
E436	Inverter high heat-sink temperature (inverter code 62)
E437	Inverter heat-sink temperature sensor fault (inverter code 65)
E438	Inverter PFC input over-current (inverter code 73)
E440	Inverter compressor slowdown - high heat-sink temperature (inverter code 13)
E441	Inverter compressor slowdown - high compressor current (inverter code 14)
E443	Unit code to inverter model mismatch
E444	Reversing valve relay or solenoid fault
E446	Low suction pressure fault
E600	Load shed event
E601	Low ambient operational lockout
Green & Red alternating FAST flash	Coil (defrost) sensor problem

All Lennox Heat Pump error codes →

Lennox code E442: homeowner questions

What does Lennox code E442 mean?

Compressor top cap switch strikes lockout. Compressor thermal protection opened five times within one hour; outdoor unit locked out. S30/S40 thermostat alert code 442 (shown as E442 on the unit control display).

Is it safe to keep using my heat pump with code E442?

It depends on the cause. The heat pump 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 E442 myself?

You can try one reset (power off for 30 seconds, then on). If Lennox code E442 comes back, the cause is still there and a licensed technician should check it.

Who can fix Lennox code E442 near me?

Aurora Star Tech Inc. repairs Lennox heat pumps in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.

Homeowner help: AC Running But Not Cooling: What to Check · Heat Pump Not Heating or Blowing Cold Air

Troubleshooting guides

Heat pump not defrosting / outdoor coil iced - Lennox EL16KP1 / ML14KP1 Lennox · Heat Pump
Low capacity or abnormal pressures - Lennox EL16KP1 / ML14KP1 Lennox · Heat Pump
Outdoor unit will not start - Lennox EL16KP1 / ML14KP1 Lennox · Heat Pump
Two horizontal lines on display (soft disable) - Lennox communicating Lennox · Heat Pump

Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.43. 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.