50401 on a Stiebel Eltron WPM heat pump manager / WPMsystem: Communication fault, exhaust air differential pressure (ventilation)
Short answer
On a Stiebel Eltron heat pump, 50401 means: Communication fault, exhaust air differential pressure (ventilation). 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: Communication fault, exhaust air differential pressure (ventilation).
Part involved: ventilation module / fans / air sensors.
When it shows: Communication fault, exhaust air differential pressure (ventilation).
Likely causes:
- Cable break, short circuit or faulty sensor, SUP and EHA fans switched off.
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: no.
Manual reset: yes - reset of heat pump via WPM after cause removed (contractor).
What you can check
- Read and note the full message code and time from the WPM display (DIAGNOSIS / NOTIFICATIONLIST if accessible without a code).
- Check the heat pump and controller circuit breakers/isolators at the consumer unit are on.
- Check the heating system pressure gauge reading is in the normal range stated by your installer.
- Check the outdoor unit air intake/discharge is not blocked by leaves, snow or ice (air source units).
What the engineer will check
- Cable break, short circuit or faulty sensor, SUP and EHA fans switched off.
Who to ask for: MVHR/ventilation-competent heat pump engineer.
What you might notice
Sources
- WPM notification list (WPM V2.9) - multilingual; English section pp.15-26 (DOC-00081866) ↗ · WPM V2.9 · page 26 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026