L1 on a Baxi heat pump: Display reads L1 with audible alarm
Short answer
On a Baxi heat pump, L1 means: Display reads L1 with audible alarm. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Geoflo Compact ground source heat pump
The manual says: Display reads L1 with audible alarm.
Part involved: water flow / pressure.
Likely causes:
- Low temperature in ground arrays because of no water flow. Remedy (manual): Bleed right-hand water pump; call plumber to investigate.
On the HP40 / Baxi Assure HP50 Monobloc ASHP
The manual says: DC generatrix low voltage protection (P6 group).
Part involved: inverter module, compressor, PFC.
Likely causes:
- As P6 group actions.
Is it safe?
On the Geoflo Compact ground source heat pump
| 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.
On the HP40 / Baxi Assure HP50 Monobloc ASHP
| 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
On the Geoflo Compact ground source heat pump
- Note the exact code shown on the controller and when it appeared.
- Read the heating system pressure gauge and report the value to your installer (the manuals quote a minimum of about 1 bar cold).
- Check the filling loop is closed.
- In freezing weather do not leave the system switched off - the manuals warn water faults left unrepaired in winter can let the pump and pipes freeze.
- If the code persists or returns, contact a heat pump engineer.
On the HP40 / Baxi Assure HP50 Monobloc ASHP
- 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
On the Geoflo Compact ground source heat pump
- Low temperature in ground arrays because of no water flow. Remedy (manual): Bleed right-hand water pump; call plumber to investigate.
Who to ask for: heating / heat pump engineer (hydraulics).
Certification: Heating/GSHP installer competence; F-gas only if refrigerant circuit opened.
On the HP40 / Baxi Assure HP50 Monobloc ASHP
- 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
- Baxi Geoflo Single Compressor Compact Heat Pump - Operation, Installation & Maintenance Instructions ↗ · Comp No TP0201 - Iss 6 - 05/07 · page 7 · 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 77 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026