P27 on a Baxi HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP: H-SEN and L-SEN connected in reverse (detected when the compressor is off)
Short answer
On a Baxi heat pump, P27 means: H-SEN and L-SEN connected in reverse (detected when the compressor is off). The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: H-SEN and L-SEN connected in reverse (detected when the compressor is off).
Part involved: refrigerant pressure / temperature.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: unknown.
Manual reset: unknown.
What you can check
- Note the exact code shown on the controller and when it appeared.
- Check the outdoor unit is not blocked by leaves, debris, snow or covers and has clear airflow.
- If the code persists or returns, contact a heat pump engineer.
What the engineer will check
- Diagnose per manufacturer service procedure (manual gives description only).
Who to ask for: heat pump / refrigeration engineer (F-gas).
Certification: F-gas certification (Category I) for refrigerant work; competence with flammable A3 refrigerant R290.
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 58 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026