F29 on a Dimplex WPM heat pump manager platform: Temperature difference: temperature difference between flow and return is too large (>12 K) or negative for defrosting
Short answer
On a Dimplex heat pump, F29 means: Temperature difference: temperature difference between flow and return is too large (>12 K) or negative for defrosting. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Temperature difference: temperature difference between flow and return is too large (>12 K) or negative for defrosting.
Part involved: Flow and return sensors.
Likely causes:
- Heating water flow rate too low.
- Overflow valve or pump size.
- Flow and return mixed up.
- Cold screed/underfloor started too quickly (GDHV).
Is it safe?
| 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
- 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
- Check heating water flow rate.
- Check overflow valve and pump size.
- Check flow/return not swapped.
- Check buffer/hydraulic layout and volume.
Who to ask for: heating 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