Daikin Altherma fault EC-04

What it means

Unit is preheating the tank. The water in the heating system and the tank is too cold to perform defrost operation, so the tank needs to be preheated electrically.

Likely causes

1. Water in heating system and tank too cold to perform defrost operation
2. Deviation of thermistor
3. Bad contact between sensor and pipe
4. Domestic hot water tank thermistor measures a higher temperature than actual (component failure)

Where to start

1. No specific check/repair procedures must be performed to solve this error code
2. Wait until preheating operation is done
3. Check domestic hot water tank thermistor