H12 on a Dimplex LA MI inverter outdoor air-to-water: Mismatch of PCB fitted to the heat pump (capacity of refrigerant PCB and water PCB do not match)
Short answer
On a Dimplex heat pump, H12 means: Mismatch of PCB fitted to the heat pump (capacity of refrigerant PCB and water PCB do not match). 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: Mismatch of PCB fitted to the heat pump (capacity of refrigerant PCB and water PCB do not match).
Part involved: Main refrigerant PCB / main water PCB.
Likely causes:
- Wrong-capacity PCB fitted during repair.
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: Clear via control panel per Dimplex article (method shown as image).
What you can check
- Note the code and contact the installer or Dimplex service.
What the engineer will check
- Isolate the heat pump from mains before any work.
- Fit correct-kW refrigerant or water PCB so both boards match.
Who to ask for: refrigeration / heat pump service engineer.
Certification: F-Gas (refrigerant handling) certification for any refrigerant-circuit work.
What you might notice
Sources
- GDHV Help Centre article: i have h12 error on my la mi heat pump what does this mean ↗ · GDHV article (modified 2023-02) · page n/a (web article) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026