Thermostat shows E06 and will not energize heating outputs; heat calls may be ignored.

Safety: This involves control wiring to heating equipment. Turn off power to the furnace/air handler and thermostat at the breaker before proceeding.

• Step 1 – Check wiring: Remove the thermostat and verify that W/W1/W2 wires are correctly landed and not touching adjacent terminals. Tighten all screws.
• Step 2 – Inspect for shorts: At the furnace control board, inspect the thermostat cable. Look for crushed or pinched sections where conductors may short to ground or each other.
• Step 3 – Test output: With power restored and E06 present, call for heat and measure voltage between R and W/W1 at the thermostat. If the thermostat does not send 24 VAC when calling for heat, the internal relay is likely failed.
• Step 4 – Bypass test (advanced): With power off, temporarily jumper R to W/W1 at the furnace control board to confirm the furnace itself operates. Remove jumper after test.
• Step 5 – Replace thermostat: If the furnace responds to a jumper but not to the thermostat, replace the thermostat main control board or entire thermostat.