H64 on a Dimplex LA MI inverter outdoor air-to-water: Refrigerant high pressure (sensor) abnormality
Short answer
On a Dimplex heat pump, H64 means: Refrigerant high pressure (sensor) abnormality. 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: Refrigerant high pressure (sensor) abnormality.
Part involved: Outdoor high pressure sensor.
When it shows: During defrost/heating, high pressure sensor output 0 V DC or 5 V DC; 4 times in 20 minutes.
Likely causes:
- Faulty connector connection.
- Faulty sensor.
- Faulty outdoor PCB.
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
- Until an engineer attends, switch on the electric backup per the Dimplex guide 'How do I switch on the backup on the LA-MI heat pump?' (GDHV help centre).
- 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 HP sensor connector and output.
- Replace HP sensor X-2511012 or refrigerant PCB.
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 h64 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