Q: About 30 seconds after the heating has been switched on, the red monitor lamp lights up and remains steady.

Possible cause: Gas cylinder or quick-closure valve in the gas line is closed, or air feed interrupted.. Check gas feed, check cowl for possible coverage, and if being used on boats, open the deck cowl.

Q: Heating switches to Fault mode after an extended period of operation.

Possible cause: Hot-air outlets blocked, gas pressure regulator iced up, or butane content in the gas cylinder too high.. Check individual outlet apertures, use de-icing system controller (EisEx), and use propane (at temperatures below 10°C in particular, butane is unsuitable for heating purposes).

Q: No control lamp lights up when the 230 V electrical operation system is switched on.

Possible cause: No supply voltage.. Check 230 V supply voltage and fuses.

Q: When the heating system is switched off, the electrical safety/drain valve opens.

Possible cause: Outside temperature below 4°C or no 12 V power supply at the drain valve.. Switch the heating on (at temperatures of about 4°C and below the drain valve will open automatically). Check 12 V supply voltage and fuses.

Q: The electrical safety/drain valve will no longer close, or water is dripping from the electrical safety/drain valve.

Possible cause: Outside temperature below 8°C, no 12 V power supply at the drain valve, or water pressure too high.. Switch the heating on (without heating operation, the drain valve will not close again until temperatures above 8°C have been reached), check 12 V supply voltage and fuses, and check pump pressure (max. 2.8 bar). If connected to a central water supply, use a pressure reducer to prevent pressures higher than 2.8 bar entering the boiler. If the issue remains unresolved, contact an authorized service agent.

Question 1

No control lamp lights up when the system is switched on (winter and summer operation).

Accepted Answer

Possible cause: Device fuse or vehicle fuse defective, open window above cowl (window switch), or low battery voltage.. Charge battery voltage (12 V), check all electrical plug connections and fuses, and close the window.

Question 2

The green indicator lamp comes on when the equipment is switched on (using the ZUC timer), but the heater is not operating.

Accepted Answer

Possible cause: Open window above cowl (window switch).. Close the window.

Question 3

The red monitor lamp flashes after the heating system has been switched on.

Accepted Answer

Possible cause: Battery voltage is too low (< 10.5 V).. Charge the battery.

Question 4

About 30 seconds after the heating has been switched on, the red monitor lamp lights up and remains steady.

Accepted Answer

Possible cause: Gas cylinder or quick-closure valve in the gas line is closed, or air feed interrupted.. Check gas feed, check cowl for possible coverage, and if being used on boats, open the deck cowl.

Question 5

Heating switches to Fault mode after an extended period of operation.

Accepted Answer

Possible cause: Hot-air outlets blocked, gas pressure regulator iced up, or butane content in the gas cylinder too high.. Check individual outlet apertures, use de-icing system controller (EisEx), and use propane (at temperatures below 10°C in particular, butane is unsuitable for heating purposes).

Question 6

No control lamp lights up when the 230 V electrical operation system is switched on.

Accepted Answer

Possible cause: No supply voltage.. Check 230 V supply voltage and fuses.

Question 7

When the heating system is switched off, the electrical safety/drain valve opens.

Accepted Answer

Possible cause: Outside temperature below 4°C or no 12 V power supply at the drain valve.. Switch the heating on (at temperatures of about 4°C and below the drain valve will open automatically). Check 12 V supply voltage and fuses.

Question 8

The electrical safety/drain valve will no longer close, or water is dripping from the electrical safety/drain valve.

Accepted Answer

Possible cause: Outside temperature below 8°C, no 12 V power supply at the drain valve, or water pressure too high.. Switch the heating on (without heating operation, the drain valve will not close again until temperatures above 8°C have been reached), check 12 V supply voltage and fuses, and check pump pressure (max. 2.8 bar). If connected to a central water supply, use a pressure reducer to prevent pressures higher than 2.8 bar entering the boiler. If the issue remains unresolved, contact an authorized service agent.

Error Code / Indicator	Symptom / Meaning	Step-by-Step DIY Fix	Suggested Actions
`N/A`	No control lamp lights up when the system is switched on (winter and summer operation). Possible Cause: Device fuse or vehicle fuse defective, open window above cowl (window switch), or low battery voltage.	Charge battery voltage (12 V), check all electrical plug connections and fuses, and close the window.	DIY Safe
`N/A`	The green indicator lamp comes on when the equipment is switched on (using the ZUC timer), but the heater is not operating. Possible Cause: Open window above cowl (window switch).	Close the window.	DIY Safe
`N/A`	The red monitor lamp flashes after the heating system has been switched on. Possible Cause: Battery voltage is too low (< 10.5 V).	Charge the battery.	DIY Safe
`N/A`	About 30 seconds after the heating has been switched on, the red monitor lamp lights up and remains steady. Possible Cause: Gas cylinder or quick-closure valve in the gas line is closed, or air feed interrupted.	Check gas feed, check cowl for possible coverage, and if being used on boats, open the deck cowl.	DIY Safe
`N/A`	Heating switches to Fault mode after an extended period of operation. Possible Cause: Hot-air outlets blocked, gas pressure regulator iced up, or butane content in the gas cylinder too high.	Check individual outlet apertures, use de-icing system controller (EisEx), and use propane (at temperatures below 10°C in particular, butane is unsuitable for heating purposes).	DIY Safe
`N/A`	No control lamp lights up when the 230 V electrical operation system is switched on. Possible Cause: No supply voltage.	Check 230 V supply voltage and fuses.	DIY Safe
`N/A`	When the heating system is switched off, the electrical safety/drain valve opens. Possible Cause: Outside temperature below 4°C or no 12 V power supply at the drain valve.	Switch the heating on (at temperatures of about 4°C and below the drain valve will open automatically). Check 12 V supply voltage and fuses.	DIY Safe
`N/A`	The electrical safety/drain valve will no longer close, or water is dripping from the electrical safety/drain valve. Possible Cause: Outside temperature below 8°C, no 12 V power supply at the drain valve, or water pressure too high.	Switch the heating on (without heating operation, the drain valve will not close again until temperatures above 8°C have been reached), check 12 V supply voltage and fuses, and check pump pressure (max. 2.8 bar). If connected to a central water supply, use a pressure reducer to prevent pressures higher than 2.8 bar entering the boiler. If the issue remains unresolved, contact an authorized service agent.	DIY Check / Tech Fallback

Truma C 3402 / C 6002

Technical Specifications

Master Troubleshooting & Diagnostics Matrix