H1 on a Worcester Bosch Bosch Compress 2000 AWF: Alarm table: Communication error between unit and IR341 (unit and inverter module) / Troubleshooting table: Communication error between PCB A inverter module and the main PCB B control board
Short answer
On a Worcester Bosch heat pump, H1 means: Alarm table: Communication error between unit and IR341 (unit and inverter module) / Troubleshooting table: Communication error between PCB A inverter module and the main PCB B control board. 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: Alarm table: Communication error between unit and IR341 (unit and inverter module) / Troubleshooting table: Communication error between PCB A inverter module and the main PCB B control board.
Part involved: inverter module to main PCB.
When it shows: Communication error between unit and IR341 (unit and inverter module).
Likely causes:
- Power not connected to PCB/secondary board (indicator light off); loose/broken wire between main and secondary PCB; faulty boards.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: Manual 13.2: switch the unit off and on again to reset the safety device; if reset fails contact dealer. Manual 11.4 warns repeated resets can cause irreversible damage.
What you can check
- Read and note the full code (and sub-code) shown on the controller and pass it to your installer.
- Manual 13.2: one off/on restart may be tried; if the code returns, stop and call an engineer - repeated resets can damage the unit.
What the engineer will check
- Check board power and indicator; check interconnecting wiring; replace main PCB and secondary board.
Who to ask for: heat pump installer / electrician.
Certification: Electrical work to BS 7671 by competent person.
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- Heat pump will not start on the Bosch Compress 2000 AWF (R32 all-in-one monobloc): 1 report
Sources
- Installation and operating instructions Compress 2000 AWF CS2000AWF 4-30 R-S/T ↗ · 6721859133 (2025/10) · page 128; 136 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026