Honeywell Thermostat Error Codes: Cool On, Heat On, E1, E2, Waiting — Fix Guide

Common Symptoms

• Thermostat display showing a message or code
• AC or heat not turning on despite being set
• Thermostat showing 'Cool On' or 'Heat On' but system not running
• System not responding after power outage
• 'Waiting' message on display with no HVAC activity

Most Likely Causes

1. 1

   Cool On (Flashing) — Compressor Time Delay

   Not an error — this is the compressor protection delay. After the AC is set to cool, the thermostat waits 5 minutes before sending the cooling signal to protect the compressor from short-cycling. If 'Cool On' is flashing, the system will turn on automatically after the delay.

2. 2

   Heat On (Flashing) — Same Protection Delay

   Same as Cool On — the thermostat is in the 5-minute protection delay before activating the heat. This is normal and does not indicate a fault.

3. 3

   E1 — Open Remote Room Sensor

   A remote room temperature sensor connected to the thermostat has an open circuit (disconnected or broken wire). Only applies to thermostats with a wired remote sensor accessory installed.

4. 4

   E2 — Shorted Remote Room Sensor

   A remote room sensor has a shorted circuit (damaged wiring or a failed sensor). The thermostat cannot read room temperature from the sensor.

5. 5

   Waiting — Temperature Differential or Recovery Mode

   The thermostat is in recovery mode (ramping the temperature toward the setpoint) or is waiting for the temperature differential to be met before cycling the equipment. This is normal operation on programmable Honeywell thermostats.

Quick DIY Checks

1. 1For Cool On / Heat On flashing: Simply wait 5 minutes. The thermostat's built-in compressor protection delay is working as designed. If the system does not turn on after 5 minutes, verify the thermostat wiring — check that the Y wire (cooling) and W wire (heating) are properly seated in their terminals.
2. 2For Waiting: Check the current room temperature vs. the setpoint. If the room is close to the setpoint (within 1–2 degrees), the thermostat may be in a 'satisfied' state. Adjust the setpoint 3 degrees warmer (heat) or cooler (cool) to force the system to run.
3. 3For E1/E2 sensor errors: These codes only appear if a remote sensor is wired to the thermostat. Trace the sensor wire from the thermostat to the sensor location. Check for disconnected, pinched, or visually damaged wiring. Reconnect or replace the sensor.

1. 4If the system isn't running despite no error codes: Check the HVAC system's power — the air handler switch should be ON, the circuit breaker untripped. Check the drain pan float switch — a full condensate pan triggers a float switch that cuts power to the thermostat's Y wire.
2. 5Reset the thermostat: For most Honeywell models, remove the thermostat from the wall plate, remove batteries for 30 seconds, reinsert, and re-mount. This clears any stored faults and memory errors.

Repair vs Replace

Recommended Tools & Parts

• Honeywell Remote Room Sensor

  Replacement remote room temperature sensor for Honeywell thermostats. Fixes E1 and E2 sensor error codes.

  $20–$50

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• Honeywell T6 Pro Programmable Thermostat

  Upgrade replacement thermostat from Honeywell. Compatible with most single-stage heating and cooling systems.

  $40–$70

  Buy on Amazon →

• Thermostat Wire (18/5)

  5-conductor 18-gauge thermostat wire. For re-running thermostat wiring when existing wire is damaged or too short.

  $15–$35

  Buy on Amazon →

• HVAC Drain Pan Float Switch

  Safety float switch that cuts power to the thermostat when the condensate drain pan is full. Replace if stuck in the open position.

  $10–$25

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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