E124
Active communicating thermostat signal missing for more than 3 minutes
This code typically points to
- Lost thermostat heartbeat
- 4-wire communication path issue
Next checks to confirm
- Check all four communicating connections
- Ohm wires
- Cycle power at thermostat
Escalation
Stops services and waits for thermostat heartbeat
Reset behavior
Clears when valid thermostat message is received.
Urgent
Fix now