Mitsubishi Ecodan fault L6

What it means

Error code displayed when THW1 detects a temperature ≤ 1ºC for 10 consecutive seconds or THW2 detects a temperature ≤ 3ºC for 10 consecutive seconds. Applicable in DHW/Heating/Cooling/LP/FS/OS modes. Exception: error code will not be displayed if FS function is disabled, or for 10 minutes after water circulation pump1 is switched on.

Likely causes

1. Insufficient system head
2. Reduced flow in primary water circuit due to faulty pump, insufficient air purge, blocked strainer, or leak in water circuit
3. Valve operation fault
4. 2-way valve (local supply) actuator fault
5. 3-way valve actuator fault
6. THW1 has become detached from its holder
7. THW1 or THW2 fault
8. FTC board failure

Where to start

1. Refer to table in section 10-6 to determine if system pump meets requirements
2. Check circulation pump (see 10-6 for how to check)
3. Open purge valve to remove trapped air