P4 on a Midea heat pump: Compressor protection against excessively high discharge temperature
Short answer
On a Midea heat pump, P4 means: Compressor protection against excessively high discharge temperature. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 4 sources
What it means
On the M-Thermal Arctic HT R290 monobloc (MHC ...WD2N7)
The manual says: Compressor protection against excessively high discharge temperature.
Likely causes:
- See R290 service manual troubleshooting (section 6) for this code.
On the M-Thermal Mono R32 (MHC ...W/D2N8-B / -B2 'Arctic')
The manual says: Discharge temperature protection.
Likely causes:
- Temperature sensor error.
- High pressure side blockage.
- Poor condenser heat exchange.
- Main PCB damaged.
On the M-Thermal Mono R32 compact (MHC ...WD2N8-C, 5/7/9/12/14/16 kW)
The manual says: High discharge temperature protection.
Likely causes:
- Same causes as P1.
- refrigerant shortage.
- TW_out, T1 or T5 sensor loose.
On the M-Thermal Split R32 (MHA outdoor + HB hydronic box)
The manual says: Discharge temperature protection.
Likely causes:
- Temperature sensor error.
- High pressure side blockage.
- Poor condenser heat exchange.
- Outdoor unit main PCB damaged.
Is it safe?
On the M-Thermal Arctic HT R290 monobloc (MHC ...WD2N7)
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
On the M-Thermal Mono R32 (MHC ...W/D2N8-B / -B2 'Arctic')
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
On the M-Thermal Mono R32 compact (MHC ...WD2N8-C, 5/7/9/12/14/16 kW)
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
On the M-Thermal Split R32 (MHA outdoor + HB hydronic box)
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Read and note the exact code shown on the controller display.
- Check the heat pump's breaker/isolator at the consumer unit is on.
- Check the outdoor unit is not blocked by leaves, debris or snow and has clear space around it.
- Restart once via the controller (OFF then ON) as the manual allows; if the code returns, call an engineer.
What the engineer will check
On the M-Thermal Arctic HT R290 monobloc (MHC ...WD2N7)
- See R290 service manual troubleshooting (section 6) for this code.
On the M-Thermal Mono R32 (MHC ...W/D2N8-B / -B2 'Arctic')
- Temperature sensor error.
- High pressure side blockage.
- Poor condenser heat exchange.
- Main PCB damaged.
On the M-Thermal Mono R32 compact (MHC ...WD2N8-C, 5/7/9/12/14/16 kW)
- Same causes as P1.
- refrigerant shortage.
- TW_out, T1 or T5 sensor loose.
On the M-Thermal Split R32 (MHA outdoor + HB hydronic box)
- Temperature sensor error.
- High pressure side blockage.
- Poor condenser heat exchange.
- Outdoor unit main PCB damaged.
Sources
- R290 M thermal Arctic HT Series Service Manual ↗ · 2025-10-15 v5 (from file name) · page 92 · Reviewed 23 September 2026
- Midea M thermal Arctic Mono (4~16kW) Service Manual ↗ · not stated (MBT Confidential) · page 65 (table); 96 (troubleshooting) · Reviewed 23 September 2026
- M-thermal Mono ATW Heat Pump Installation and Owner's Manual (5/7/9/12/14/16 kW) ↗ · 16125300001699 V4.0 · page PDF 78 (printed 75) · Reviewed 23 September 2026
- M-Thermal A Series Split R32 Service Manual (Midea CAC, 202004) ↗ · 202004 (file v31) · page 50 (table); 79 (troubleshooting) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026