H0 on a Baxi heat pump: Communication error between main control board PCB B and main control board of hydraulic module
Short answer
On a Baxi heat pump, H0 means: Communication error between main control board PCB B and main control board of hydraulic module. 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 · 3 sources
What it means
On the Assure Monobloc ASHP (Assure Mono 5/7/9/12/16)
The manual says: Communication error between main control board PCB B and main control board of hydraulic module.
Part involved: PCB communication wiring.
Likely causes:
- No connection between PCB B and hydraulic module main board; wire sequence wrong; magnetic/power interference.
On the HP40 / Baxi Assure HP50 Monobloc ASHP
The manual says: Communication fault between main board PCB B and main control board of hydraulic module.
Part involved: PCB communication wiring.
Likely causes:
- Wire not connected between PCB B and hydraulic module main board; communication wire sequence incorrect; strong magnetic/power interference.
On the HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP (R290)
The manual says: Communication error on Main Control PCB.
Part involved: PCB communication wiring.
Is it safe?
On the Assure Monobloc ASHP (Assure Mono 5/7/9/12/16)
| 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: Power OFF/ON after correcting cause (ISM 13.4).
On the HP40 / Baxi Assure HP50 Monobloc ASHP
| 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: Installer: correct cause then power OFF/ON (ISM 13.4).
On the HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP (R290)
| 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.
- If the code persists or returns, contact a heat pump engineer.
What the engineer will check
On the Assure Monobloc ASHP (Assure Mono 5/7/9/12/16)
- No connection between PCB B and hydraulic module main board; wire sequence wrong; magnetic/power interference.
Who to ask for: heat pump engineer (controls / sensors).
Certification: Manufacturer-trained heat pump engineer.
On the HP40 / Baxi Assure HP50 Monobloc ASHP
- Wire not connected between PCB B and hydraulic module main board; communication wire sequence incorrect; strong magnetic/power interference.
Who to ask for: heat pump engineer (controls / sensors).
Certification: Manufacturer-trained heat pump engineer.
On the HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP (R290)
- 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 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 72 · 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 73, 75 · Reviewed 23 September 2026
- 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 57 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026