Truma Water Heater: “W42H”
warning RV water heater fault codes
What it means
Roof-window safety warning on the Combi: a window above the heater's exhaust cowl is open and the window switch has shut the heater down to prevent exhaust gas from entering the living space. The heater will not run until the window is closed.
Most likely causes
- Skylight/window above the exhaust cowl is open most likely
- Faulty or stuck window switch reporting 'open' less common
- Window-switch wiring fault rare
Safe checks you can do yourself
- Close the roof window/skylight located above the heater's exhaust cowl.
- Confirm the window is fully seated so the switch registers it as closed.
- Check whether the same window switch is shared with the cooktop, which can also trip it.
How to reset / clear W42H
- Close the window; the heater should allow restart automatically.
- If needed, switch the heater off and on at the CP plus panel after closing the window.
When to call a technician
The window is confirmed closed but W42H stays on, indicating a defective window switch or wiring.
Applies to
Truma Combi 4 / Combi 6 · Truma Combi 4 E / Combi 6 E · CP plus control panel
FAQ
What does Truma Water Heater code "W42H" mean?
Roof-window safety warning on the Combi: a window above the heater's exhaust cowl is open and the window switch has shut the heater down to prevent exhaust gas from entering the living space. The heater will not run until the window is closed.
How do I reset Truma Water Heater W42H?
Close the window; the heater should allow restart automatically. If needed, switch the heater off and on at the CP plus panel after closing the window.
What is the most common cause of W42H on a Truma Water Heater?
The most likely cause is skylight/window above the exhaust cowl is open.
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Sources
- Truma CP plus Operating Instructions — Troubleshooting guide for Combi gas heater (H) — CP plus operating instructions p.17, fault code W42H (Truma (OEM-hosted, Imperial Outdoors))
Note: Applies only to installations fitted with a window switch above the cowl; not all coaches have this interlock.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.