Heat pumps · Error codes · Baxi
bABaxi · HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP (R290)
bA on a Baxi HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP: T4 sensor out of operation range protection
Short answer
On a Baxi heat pump, bA means: T4 sensor out of operation range protection. The heat pump keeps running.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: T4 sensor out of operation range protection.
Part involved: protection function.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The heat pump keeps running.
Resetting itself: unknown.
Manual reset: unknown.
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
- Diagnose per manufacturer service procedure (manual gives description only).
Who to ask for: heat pump engineer (controls / sensors).
Certification: Manufacturer-trained heat pump engineer.
What you might notice
Sources
- Installation, user and service manual - Reversible monobloc air-to-water heat pump, outdoor unit HP60-4-1-PHMB to HP60-13-3-PHMB ↗ · 7888668 - v03 - 17072025 · page 60 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026