Mitsubishi Ecodan fault P1

What it means

Failure of indoor unit temperature thermistor TH1. Refer to error codes (P1/P2/L5/LD) for diagnosis and action.

Likely causes

1. Connector/terminal wire has become detached or loose wiring
2. Thermistor fault
3. FTC board failure
4. Thermistor on the wireless remote controller or main remote controller may be defective (when Room temp. is chosen for Heating operation and Main remote controller or Room RC 1-8 is chosen for Room Sensor setting)
5. Incorrect setting of the DIP switch(es)
6. Failed thermistor TH1A (Zone 1 room temp)
7. Failed thermistor TH2 (Ref. liquid temp)
8. Failed thermistor THW1 (Flow water temp)
9. Failed thermistor THW2 (Return water temp)
10. Failed thermistor THWB1 (Boiler flow water temp)
11. Failed thermistor THW5 (DHW tank water temp)
12. Failed thermistor THWB2 (Boiler return water temp)
13. Failed thermistor TH1B (Zone 2 room temp)
14. Failed thermistor THW6 (Zone 1 flow water temp)
15. Failed thermistor THW7 (Zone 1 return water temp)
16. Failed thermistor THW8 (Zone 2 flow water temp)
17. Failed thermistor THW9 (Zone 2 return water temp)

Where to start

1. Visually check the terminals and connections and reattach as appropriate
2. Check resistance of thermistor against table in section 10-6
3. Compare FTC detected temperature to hand held detector