Honeywell Thermostat Error Codes
Complete list of Honeywell thermostat error codes with causes and how to fix them.
E1
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Honeywell Thermostat error code E1: Compressor protection — short-cycle lockout …
Technician Required
E2
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Honeywell Thermostat error code E2: Auxiliary heat lockout.
✓ DIY Possible
E3
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Honeywell Thermostat error code E3: Aux/EM heat only — heat pump malfunction.
✓ DIY Possible
E4
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Honeywell Thermostat error code E4: Auxiliary heat lockout due to outdoor …
✓ DIY Possible
E5
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Honeywell Thermostat error code E5: Aux/Emergency heat in use — heat pump not …
✓ DIY Possible
E6
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Honeywell Thermostat error code E6: Low battery warning — replace batteries.
Technician Required
E9
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Honeywell Thermostat error code E9: Failed to reach setpoint — HVAC performance …
Technician Required
ERR1
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Honeywell Thermostat error code Err1: Communication failure with equipment.
Technician Required
ERR2
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Honeywell Thermostat error code Err2: Indoor temperature sensor failure.
✓ DIY Possible
ERR3
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Honeywell Thermostat error code Err3: Outdoor temperature sensor failure.
✓ DIY Possible
ERR4
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Honeywell Thermostat error code Err4: Humidity sensor failure.
✓ DIY Possible
HI
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Honeywell Thermostat error code HI: Current temperature above display range.
Technician Required
LO
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Honeywell Thermostat error code LO: Current temperature below display range.
Technician Required