IWS-RED-LED-ON on a Stiebel Eltron heat pump: Red LED on the IWS illuminates: more than 5 faults within 2 hours run; appliance shut down permanently until reset
Short answer
On a Stiebel Eltron heat pump, IWS-RED-LED-ON means: Red LED on the IWS illuminates: more than 5 faults within 2 hours run; appliance shut down permanently until reset. 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: Red LED on the IWS illuminates: more than 5 faults within 2 hours run; appliance shut down permanently until reset.
Part involved: IWS integral heat pump controller.
When it shows: Red LED on the IWS illuminates: more than 5 faults within 2 hours run; appliance shut down permanently until reset.
Likely causes:
- High pressure fault.
- Low pressure fault.
- Central fault.
- Hardware faults on the IWS (see notification list on WPM).
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: yes - reset via IWS reset button / heat pump reset in WPM (contractor).
What you can check
- Note the message code on the WPM display.
- Check heat pump breakers/isolator at the consumer unit are on.
What the engineer will check
- IWS is inside the appliance control panel - opening required; check DIP switch (WP-Typ, BA) settings, reset button, notification list on WPM.
Who to ask for: Heat pump service engineer.
What you might notice
Sources
- OPERATION AND INSTALLATION Air source heat pump WPL 15 AS / 15 ACS / 20 A / 20 AC / 25 AS / 25 ACS / 25 A / 25 AC ↗ · A 329692-43364-9647 · page 27 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026