F12 on a Dimplex heat pump: Refrigerant high pressure switch activated to protect the system
Short answer
On a Dimplex heat pump, F12 means: Refrigerant high pressure switch activated to protect the system. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the LA MI inverter outdoor air-to-water (LA 6/9/12/16 MI)
The manual says: Refrigerant high pressure switch activated to protect the system.
Part involved: High pressure switch.
When it shows: Pressure >= 4.5 MPa detected by outdoor HP switch; 4 times in 20 minutes.
Likely causes:
- Insufficient water flow.
- Isolation valves left closed.
- Air / low system pressure / blocked strainer.
- Faulty HP switch or refrigerant PCB.
- Refrigerant overcharge.
On the WPM heat pump manager platform (error-code grouping)
The manual says: Inverter: a fault has occurred on the inverter.
Part involved: Compressor inverter.
Likely causes:
- Inverter fault.
Is it safe?
On the LA MI inverter outdoor air-to-water (LA 6/9/12/16 MI)
| 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).
On the WPM heat pump manager platform (error-code grouping)
| 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: After rectifying the fault the heat pump can be restarted; switching off the control voltage also acknowledges the fault (WPM Touch p.54). On text-display WPMs press Esc to acknowledge (EconPlus EN-16).
Manual reset: De-energise the device for 2 minutes, then restart.
What you can check
On the LA MI inverter outdoor air-to-water (LA 6/9/12/16 MI)
- Check the heating system pressure gauge reads about 1.0-1.5 bar.
- Note the code and contact the installer or Dimplex service.
On the WPM heat pump manager platform (error-code grouping)
- The manual's action is to de-energise the device for 2 minutes: switch the heat pump off at its isolator/breaker for 2 minutes, switch back on; if F12 returns, leave it and call after-sales.
- Note the fault code, the heat pump model (type plate) and controller software version shown in operating data, and contact the installer/Dimplex service.
What the engineer will check
On the LA MI inverter outdoor air-to-water (LA 6/9/12/16 MI)
- Isolate the heat pump from mains before any work.
- Flow checks as H62.
- Check isolation valves open.
- Check HP switch X-2511013 (F-Gas gauge test <45 bar).
Who to ask for: refrigeration / heat pump service engineer.
Certification: F-Gas (refrigerant handling) certification for any refrigerant-circuit work.
On the WPM heat pump manager platform (error-code grouping)
- Diagnose inverter drive, supply voltage and compressor per service documentation.
Who to ask for: heat pump service engineer / electrical.
Certification: Electrical competence (Part P / qualified electrician) for work inside control panels.
What you might notice
Sources
- GDHV Help Centre article: i have f12 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
- Dimplex WPM Touch heat pump manager - Operating instructions for users and specialists (Order no. 452117.66.02-EN, WPM3.13 / Display 1.15) ↗ · 452117.66.02-EN FD 0302 · page 54 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026