McLouis boiler not producing hot water: what's going on?

McLouis has been building campervans and motorhomes in various segments for years. Depending on the model and year of manufacture, your vehicle may be equipped with a Truma Combi (combination of heater and water heater), an Alde system (liquid heating with hot water boiler, often in the more expensive models) or a separate Truma water heater (such as the Truma Boiler Elektro or Gas). Each system has its own typical faults.

With a Truma Combi, the most common cause of no hot water is a gas ignition problem. The burner may be dirty, the ignition electrode worn, or the gas pressure too low. If the appliance works on 230V but not on gas, it is often due to the gas regulator or the ignition. With an Alde system, the boiler is usually linked to the central heating boiler. No hot water can then indicate an empty boiler (for example after draining for winter), a faulty circulation pump or a fault in the 12V circuit that controls the pump.

Diagnosis by power source

First check which energy source your water heater should be working on. Many appliances have a selector switch for gas, 230V or both. Is it set correctly? Then check the fuses and the residual current device in the motorhome. With a Truma Combi on gas, you should hear a clicking sound from the ignition and then a blue flame. If this does not happen, the ignition unit may be faulty or the burner blocked. With an Alde system, the circulation pump should hum softly. If you hear nothing, the pump may be broken or not receiving power.

Another often overlooked point is the safety valve or pressure relief valve. If it keeps leaking, the pressure in the system drops and the water heater cannot heat up properly. Also check that the water heater is filled with water. After a winter shutdown, there may be air in the pipes, causing the water heater to run dry and the safety device to activate.

• Check the energy selection: gas, 230V or both.
• Check fuses and residual current device.
• Listen for ignition (Truma) or circulation pump (Alde).
• Check water pressure and fill level of the water heater.
• Inspect the pressure relief valve for leaks.

For a more detailed explanation of all possible causes for motorhomes in general, read our page on motorhome water heater not producing hot water.

What should a repair cost?

The costs depend heavily on the part and the garage's hourly rate. A new ignition unit for a Truma Combi quickly costs between 150 and 300 euros, excluding installation. A circulation pump for an Alde system is in the same range. If the burner is heavily soiled, a cleaning service may suffice, which is usually cheaper. Expect to pay 60 to 90 euros per hour for a diagnosis at a specialist motorhome garage. Sometimes the problem can be easily solved yourself, but if in doubt, professional help is recommended.