F20 on a Dimplex heat pump: Compressor overheating protection activated
Short answer
On a Dimplex heat pump, F20 means: Compressor overheating protection activated. 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: Compressor overheating protection activated.
Part involved: Compressor tank temperature sensor.
When it shows: Compressor tank temperature above 112C.
Likely causes:
- Faulty compressor tank temperature sensor.
- 2/3-way valve closed.
- Refrigerant shortage (leak).
- Clogged expansion valve or strainer.
- Faulty refrigerant PCB.
- Faulty compressor.
On the WPM heat pump manager platform (error-code grouping)
The manual says: Defrost: defrosting of the air-to-water heat pump could not be initiated or could not be ended correctly. There is a wide range of possible causes.
Part involved: Defrost control / reverse-cycle valve / flow.
When it shows: Flow temperature <18C at defrost: defrost halted, retried after 15 min; second failure activates fault, compressor blocked, 2nd heat generator enabled (GDHV).
Likely causes:
- Heating water flow rate too low.
- Heating water pressure too low / air in system.
- Flow temperature below 18C so defrost aborts twice (GDHV).
- Flow/return spread >= 12K or negative (GDHV).
- Insufficient system volume/buffer, cold screed at first start (GDHV).
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? | Partly |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
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: Acknowledge after rectification.
What you can check
On the LA MI inverter outdoor air-to-water (LA 6/9/12/16 MI)
- Note the code and contact the installer or Dimplex service.
On the WPM heat pump manager platform (error-code grouping)
- Check the outdoor unit is not blocked by snow or debris.
- Check the heating system pressure gauge reading (typically 1.0-1.5 bar).
- 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.
- Check CN-TANK sensor resistance.
- Leak check / charge (F-Gas).
- Check expansion valve X-2511026.
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)
- Check heating water flow rate vs nominal.
- Check heating water pressure and air.
- Check flow and return temperatures during defrost.
- Check strainer/magnetic filter.
- Hot-gas-defrost models: refrigerant engineer.
Who to ask for: 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 f20 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 55 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026