L8 on a Baxi HP40 / Baxi Assure HP50 Monobloc ASHP: Speed difference >15Hz protection between the front and the back clock (P6 group)
Short answer
On a Baxi heat pump, L8 means: Speed difference >15Hz protection between the front and the back clock (P6 group). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Speed difference >15Hz protection between the front and the back clock (P6 group).
Part involved: inverter module, compressor, PFC.
Likely causes:
- As P6 group actions.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: unknown.
Manual reset: Installer: correct cause then power OFF/ON (ISM 13.4).
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.
- Check the heat pump's consumer-unit breaker / isolator is on (do not open any panels).
- If the code persists or returns, contact a heat pump engineer.
What the engineer will check
- As P6 group actions.
Who to ask for: heat pump engineer with electrical competence.
Certification: Qualified electrician / manufacturer-trained heat pump engineer; F-gas if refrigerant circuit is opened.
What you might notice
Sources
- Installation and Service Manual - Heat Pump air/water 'inverter' HP40/50-4-1PHMB to HP40/50-13-3PHMB (United Kingdom) ↗ · 784570-01 (v1) · page 77 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026