Pb on a Midea heat pump: Anti-freezing control running (indicator)
Short answer
On a Midea heat pump, Pb means: Anti-freezing control running (indicator). The heat pump keeps running. 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: Anti-freezing control running (indicator).
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: Water side heat exchanger anti-freeze protection.
Likely causes:
- Normal system protection.
- Temperature sensor not connected properly or has malfunctioned.
- Hydronic system main PCB damaged.
On the M-Thermal Mono R32 compact (MHC ...WD2N8-C, 5/7/9/12/14/16 kW)
The manual says: Anti-freeze mode protection.
Likely causes:
- Normal protection.
- unit returns to normal operation automatically.
On the M-Thermal Split R32 (MHA outdoor + HB hydronic box)
The manual says: Water side heat exchanger anti-freeze protection.
Likely causes:
- Normal system protection.
- Temperature sensor not connected properly or has malfunctioned.
- Hydronic box main PCB damaged.
Is it safe?
On the M-Thermal Arctic HT R290 monobloc (MHC ...WD2N7)
| Does the heat pump stop? | No |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The heat pump keeps running.
On the M-Thermal Mono R32 (MHC ...W/D2N8-B / -B2 'Arctic')
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
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 | Information only |
| Engineer needed? | No |
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 | Information only |
| Engineer needed? | No |
The heat pump stops until the fault clears or is reset.
What you can check
- Read the display; this is a protection/indication state and the manual says the unit returns to normal automatically.
- Keep the heat pump powered in cold weather so frost protection can run.
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')
- Normal system protection.
- Temperature sensor not connected properly or has malfunctioned.
- Hydronic system main PCB damaged.
On the M-Thermal Mono R32 compact (MHC ...WD2N8-C, 5/7/9/12/14/16 kW)
- Normal protection.
- unit returns to normal operation automatically.
On the M-Thermal Split R32 (MHA outdoor + HB hydronic box)
- Normal system protection.
- Temperature sensor not connected properly or has malfunctioned.
- Hydronic box main PCB damaged.
Sources
- R290 M thermal Arctic HT Series Service Manual ↗ · 2025-10-15 v5 (from file name) · page 93 · Reviewed 23 September 2026
- Midea M thermal Arctic Mono (4~16kW) Service Manual ↗ · not stated (MBT Confidential) · page 65 (table); 119 (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 79 (printed 76) · Reviewed 23 September 2026
- M-Thermal A Series Split R32 Service Manual (Midea CAC, 202004) ↗ · 202004 (file v31) · page 51 (table); 108 (troubleshooting) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026