Air-source heat pump outdoor unit beside a house in the snow
Generic photo: PeterEastern · CC BY-SA 4.0

Heat pump: emergency heat (EM) or aux selected but no heat comes out

Emergency heat relies on the E/AUX/W2 wiring reaching the air handler, the strip breakers being on, and the strips' sequencers and limits working. Work from the thermostat outward: is the call leaving the thermostat, is it reaching the heater, does the heater have power?

Cross-checked ~45 min moderateBrands: All

Before you start

  • Strip heat is 240 V high current: CAUTION; lock out all air handler breakers before opening the heater section
  • Do not jumper limits
  • Refrigerant faults that caused the switch to EM are BLOCKED: refer

Diagnostic steps

Unlock all 7 steps with expected values

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Heat pump: emergency heat (EM) or aux selected but no heat comes out · OnCall Tech