Truma Furnace: “W25H–W29H”
warning RV furnace fault codes
What it means
VarioHeat voltage and airflow warnings: W25H = overvoltage above ~16.4 V; W26H = undervoltage below ~10 V; W27H = warm-air outlets or circulated-air intake blocked (or end outlet closed); W29H = imminent undervoltage below ~10.4 V. These let the furnace warn before a hard shutdown.
Most likely causes
- Low or failing house battery (W26H / W29H) most likely
- Blocked warm-air outlets or return-air intake (W27H) common
- Charger/converter pushing voltage too high (W25H) less common
- Closed or obstructed end outlet on a duct run (W27H) less common
Safe checks you can do yourself
- For W26H/W29H, check battery state of charge and charge or replace the battery.
- For W25H, check the charger/converter output for overvoltage.
- For W27H, make sure warm-air outlets are open and the return-air grille/filter is clear.
- Confirm no furniture, bedding or storage is blocking ducts or intakes.
How to reset / clear W25H–W29H
- Correct the voltage or airflow condition.
- The warning clears automatically once voltage and airflow return to normal; if not, power-cycle the CP plus panel.
When to call a technician
Battery voltage and airflow are confirmed good but the warnings persist, suggesting a sensor or board fault.
Applies to
Truma VarioHeat eco · Truma VarioHeat comfort · CP plus control panel
FAQ
What does Truma Furnace code "W25H–W29H" mean?
VarioHeat voltage and airflow warnings: W25H = overvoltage above ~16.4 V; W26H = undervoltage below ~10 V; W27H = warm-air outlets or circulated-air intake blocked (or end outlet closed); W29H = imminent undervoltage below ~10.4 V. These let the furnace warn before a hard shutdown.
How do I reset Truma Furnace W25H–W29H?
Correct the voltage or airflow condition. The warning clears automatically once voltage and airflow return to normal; if not, power-cycle the CP plus panel.
What is the most common cause of W25H–W29H on a Truma Furnace?
The most likely cause is low or failing house battery (w26h / w29h).
Related · Truma furnace
VarioHeat ignition/flame fault: the furnace released gas and… E43H
Over-voltage: the supply voltage to the heater is too high (… E44H
Under-voltage: the supply voltage to the heater is too low (… E112H / E212H
Gas/flame fault group: the burner did not ignite or the flam… W18H
Warm-air outlet or circulated-air (return air) intake is blo…
Sources
- Truma CP plus VarioHeat Operating Instructions — Troubleshooting Chart VarioHeat (H) — CP plus VarioHeat troubleshooting chart, codes W25H/W26H/W27H/W29H (Truma (OEM-hosted, ManualsLib))
- Truma Tech Tip: Common VarioHeat Error Codes — VarioHeat error-code tech tip (W27H, W29H) (Truma North America)
Note: Voltage thresholds are nominal values from the Truma chart and may vary slightly by firmware/market. W18H/W17H/E43H/E44H/E112H are covered elsewhere and excluded.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.