Heat pumps · Error codes · Baxi
PbBaxi
Pb on a Baxi heat pump: Anti-freeze mode protection
Short answer
On a Baxi heat pump, Pb means: Anti-freeze mode protection. The heat pump keeps running. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Assure Monobloc ASHP (Assure Mono 5/7/9/12/16)
The manual says: Anti-freeze mode protection.
Part involved: protection function.
Likely causes:
- Unit will return to normal operation automatically.
On the HP40 / Baxi Assure HP50 Monobloc ASHP
The manual says: Anti freeze mode.
Part involved: protection function.
Likely causes:
- Unit will return to normal operation automatically.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The heat pump keeps running.
Resetting itself: yes.
Manual reset: not required.
What you can check
- No action normally needed - the manual says the unit returns to normal operation automatically.
- Check the outdoor unit is not blocked by snow or ice.
What the engineer will check
- Unit will return to normal operation automatically.
Who to ask for: heat pump engineer (controls / sensors).
Certification: Manufacturer-trained heat pump engineer.
What you might notice
Sources
- Installation and owner's manual - Heat Pump air/water 'inverter' Assure Mono 5, 7, 9, 12, 16 ↗ · Back cover shows '7762758 - v05 - 19082020' (same number as the Assure Split manual - probably shared back-cover artwork) · page 76 · Reviewed 23 September 2026
- Installation and Service Manual - Heat Pump air/water 'inverter' HP40/50-4-1PHMB to HP40/50-13-3PHMB (United Kingdom) ↗ · 784570-01 (v1) · page 74 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026