Thermostat displays E20 and may not control emergency heat correctly on heat pump systems.

Safety first: Turn off power to the air handler and heat strips at the breaker; electric heat strips draw high current.

• Step 1 – Verify system type: Confirm in thermostat settings that the system is configured as a heat pump with auxiliary/emergency heat.
• Step 2 – Inspect Aux/E wiring: At the thermostat and air handler, ensure the Aux/E or W2 terminal is wired correctly to the auxiliary heat relay.
• Step 3 – Test emergency heat mode: Manually switch the thermostat to Emergency Heat and call for heat. If the air handler does not energize the strips, suspect a relay or wiring issue.
• Step 4 – Check air handler board: Inspect the Carrier air handler control board for burnt relays or loose connections to the heat strip contactors.
• Step 5 – Professional diagnosis: Testing heat strip circuits involves high voltage and high current; have a technician verify and repair any failed components.