F28 on a Dimplex WPM heat pump manager platform: High pressure: the heat pump has been switched off by the high pressure sensor or pressure switch
Short answer
On a Dimplex heat pump, F28 means: High pressure: the heat pump has been switched off by the high pressure sensor or pressure switch. 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: High pressure: the heat pump has been switched off by the high pressure sensor or pressure switch.
Part involved: High-pressure sensor/switch.
Likely causes:
- Heating curve too high.
- Heating water flow rate too low.
- Overflow valve setting.
- Isolation valves closed, air in system, low system pressure, blocked strainer (GDHV).
Is it safe?
| 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: Acknowledge after rectification.
What you can check
- Check the heating system pressure gauge (typically 1.0-1.5 bar); if low, ask the installer.
- Lower the heating curve a couple of degrees on the controller (GDHV).
- Power the heat pump off at the isolator for 30 minutes and back on (GDHV) - if it recurs, call the installer.
- 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
- Set heating curve lower.
- Increase heating water flow rate.
- Check overflow valve.
- Check isolation valves open and strainer/mag filter clean.
- Bleed air / re-pressurise system.
Who to ask for: heating engineer / heat pump service engineer.
What you might notice
Sources
- 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