H90 on a Dimplex LA MI inverter outdoor air-to-water: Communication error between main water PCB and main fridge (refrigerant) PCB
Short answer
On a Dimplex heat pump, H90 means: Communication error between main water PCB and main fridge (refrigerant) PCB. 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: Communication error between main water PCB and main fridge (refrigerant) PCB.
Part involved: Water PCB / refrigerant PCB interconnection.
When it shows: Data received from outdoor PCB abnormal for 1 minute after operation.
Likely causes:
- Faulty fridge PCB.
- Faulty water PCB.
- Wrong wiring.
- Broken connection wire.
- Disturbed power supply waveform.
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.
- Check 3-wire link (1 black, 2 white, 3 red) between PCBs.
- Replace PCB as diagnosed.
Who to ask for: heat pump service engineer / heating engineer.
Certification: Electrical competence (Part P / qualified electrician) for work inside control panels.
What you might notice
Sources
- GDHV Help Centre article: i have h90 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