IWS-RED-LED-FLASHING on a Stiebel Eltron heat pump: Red LED on the IWS (integral heat pump controller) flashes: single fault; appliance shut down and restarts after 10 minutes
Short answer
On a Stiebel Eltron heat pump, IWS-RED-LED-FLASHING means: Red LED on the IWS (integral heat pump controller) flashes: single fault; appliance shut down and restarts after 10 minutes. 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 (integral heat pump controller) flashes: single fault; appliance shut down and restarts after 10 minutes.
Part involved: IWS integral heat pump controller.
When it shows: Red LED on the IWS (integral heat pump controller) flashes: single fault; appliance shut down and restarts after 10 minutes.
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 | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: yes (after 10 min).
Manual reset: no.
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