Truma Combi furnace and water heater fault codes
A single LP unit that heats the coach air and a 2.6 gallon water tank. The eco plus and comfort plus versions add 120V heating elements. Faults show on the CP plus panel as W (warning, keeps running) or E (error, stops). Write the code down before you reset: turning the panel off and on clears it.
Truma Combi code W 17 H
Hot water mode selected with an empty tank. Shut it off and let it cool fully. Fill the tank (open a hot tap until it runs steady), then restart.
Truma Combi code W 18 H
Warm air outlet or circulated air intake blocked. Open every duct outlet, clear the return air intake, check for a crushed duct under a slide or behind cargo.
Truma Combi code E 18 H
Circulated air intake blocked, unit stopped. Clear the intake and the warm air outlets. If it comes back with everything open, the air sensor or electronics are at fault.
Truma Combi code E 21 H
Room temperature sensor or its cable. Check the sensor plug and cable at the panel location. Replace the sensor.
Truma Combi code W 24 H
Battery dropping toward cutoff, below 10.4V. Charge the battery. Check voltage at the Combi plug under load, not at the battery.
Truma Combi code E 41 H
Electronics locked out after repeated overheating. Fix the cause first (air blocked, empty tank, bad thermostat plate). Unlocking needs the Truma service tool on some software versions.
Truma Combi code E 43 H
Overvoltage, above 16.4V. Check the converter or charger output and any solar controller. Look for AC ripple on the 12V.
Truma Combi code E 44 H
Undervoltage, below 10.0V. Charge or replace the battery. Check the 12V feed and ground for drop under load.
Truma Combi code W 45 H
No 120V to the heating elements, or overheat protection tripped (eco plus and comfort plus). Confirm 120V at the unit and the breaker. If the 120V is good, let it cool and press the overheat reset on the unit.
Truma Combi code W 255 H
No 12V to the Combi, or no connection between the Combi and the panel. Check the 12V fuse and plug at the unit, then the panel cable at both ends. A chafed panel cable under the floor does this.
Truma Combi: E 112 H / E 202 H / E 211 H
No gas or overheat: cylinder closed, shut-off valve closed, or overheat protection tripped. Open the cylinder and the inline shut-off. Check LP pressure at the stove. If gas is good: cool the unit, fill the tank with cold water, clear every outlet and intake, restart.
Truma Combi code E 212 H
Combustion air intake or exhaust blocked, gas valve closed, regulator fault, overheat, or electronics. Clear the outside intake and exhaust (leaves, mud, ice, a bug screen). Check LP pressure. Cool and reset. If it still returns with gas and air proven, the electronics are at fault.
Truma Combi: E 121 H / E 122 H
Flame lost or unstable during a run. LP pressure under load, exhaust restriction, ignitor and electrode condition, gas solenoid. Check the unit's ground connection.
Truma Combi: E 2 H / E 16 H
No flame: gas off, air intake or exhaust blocked. Open the cylinder and valves, clear the outside intake and exhaust. VarioHeat runs on propane only.
Truma Combi code W 27 H
Circulated air intake or warm air outlet blocked. Open the outlets and clear the intake.
Truma Combi code W 29 H
Battery below 10.4V. Charge the battery, check voltage at the unit.
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Full field guide: Truma Combi furnace and water heater
Codes come from the maker manuals and public service sheets. Your model's own chart always wins, and LP and 120 volt work belongs to a qualified technician.