P2 on a Mitsubishi Electric heat pump: Thermistor (Ref. liquid temp.) (TH2) failure (FTC2: Refrigerant liquid pipe (TH2) sensor error)
Short answer
On a Mitsubishi Electric heat pump, P2 means: Thermistor (Ref. liquid temp.) (TH2) failure (FTC2: Refrigerant liquid pipe (TH2) sensor error). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Ecodan
The manual says: Thermistor (Ref. liquid temp.) (TH2) failure (FTC2: Refrigerant liquid pipe (TH2) sensor error).
Part involved: Refrigerant liquid thermistor TH2 (at plate heat exchanger).
When it shows: TH2 open (-39C or below) or short (88.5C or above); not displayed during and 10 min after defrost.
Likely causes:
- 1 Connector/terminal detached; 2 Thermistor fault; 3 FTC board failure.
On the Ecodan Co2 Quhz
The manual says: Indoor unit temperature thermistor (TH2) failure.
Part involved: TH2.
When it shows: Thermistor open or short.
Likely causes:
- Thermistor open/short; FTC board failure.
Is it safe?
On the Ecodan
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Not stated as auto-resetting; code remains until reset.
Manual reset: Installation manuals: press F4 (RESET) then F3 (Yes) on the main remote controller (older controllers: hold button E for 3 s); 'To cancel error codes please switch system off'. Fix the cause first.
On the Ecodan Co2 Quhz
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Not stated as auto-recovering.
Manual reset: Press F4 (Reset) then F3 (Yes) on the main remote controller, or switch system off (installation manual).
What you can check
- Note the code, unit and ref. address shown on the main remote controller and contact your installer (Mitsubishi user manuals: 'Make a note of the error code number and contact installer'). Check the heat pump breaker/isolator at the consumer unit is on and read the primary system pressure gauge (if fitted) so you can report it. A single reset from the main remote controller (RESET, then Yes) may be tried; if the code returns, do not keep resetting. Do not open the outdoor unit, cylinder/hydrobox or any casing.
What the engineer will check
On the Ecodan
- Check resistance across the thermistor; check connections; replace board.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan Co2 Quhz
- Refer to P1/L5 actions.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
What you might notice
What owners and engineers report
18 owner and engineer reports mention this.
- No heating on the Ecodan: 9 reports
- No hot water on the Ecodan: 9 reports
Sources
- Ecodan EHPT20X-MEHEW Service Manual (OCH814A) ↗ · OCH814A · page 60 (10-4 Self-diagnosis and action) · Reviewed 23 September 2026
- Ecodan EHPT20Q VM2EA Service Manual (GCH15010C) ↗ · GCH15010C · page 40 (10-4 Self diagnosis and action) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026