Things you should know about RV water heaters

Washing your hands, washing dishes, or even showering – if you travel with a caravan, you appreciate when hot water is available in the vehicle quickly and easily. We all know that caravans differ considerably, but so do RV water heaters. This guide gives you an overview.

Types of water heating

Appliances to heat water in caravans run on gas, electricity, diesel or a mixture of energy types. Some water heaters even use warmth from heaters to generate hot water. Depending on what type of vehicle you have and your personal water requirements, various Truma appliances may be of interest to you: Therme, Boiler or Combi heater.

Truma AquaGo

Truma AquaGo is an instant water heater that keeps the chosen water temperature constant – just like at home. Hot water flows as soon as you open the tap. No long waiting times. AquaGo runs on gas and is available in three different versions.


  • Endless hot water
  • Intuitive operation
  • Easy to maintain with decalcification tablets
  • Upgrade from basis model to AquaGo comfort possible


  • Requires maintenance
  • Must be winterised
  • Freshwater tank could become empty if you shower for too long

Boiler: large capacity, fast heating

If you also want to shower in your caravan, you should perhaps consider a boiler as a water heater. With a capacity of 14 litres, it holds enough hot water for two people to shower one after the other. Boilers run on gas, electricity, or a mixture of gas and electricity, making them suitable for caravans and motor homes.

Thanks to modern technology, they are so compact that they require very little installation space. For example, with the UltraRapid Gas, you don’t need mains current. A powerful gas burner heats the water in about 45 minutes. If you want hot water faster than this, you need a boiler with an additional electric heating element. This reduces the heating time to about 30 minutes.

An electric boiler heats water just with electricity – and it keeps the water hot for a long time. The Truma Boiler Electric is so well insulated with special foam made from expanded polypropylene (EPP) that the temperature falls by just one degree per hour.


  • Large capacity, sufficient water for showering
  • Different modes of operation possible (gas, electric, mixed mode)
  • Fast heating, little heat loss


  • Electric boiler completely reliant on mains current

Combination appliances: heating and hot water in one

A combination heater is a good alternative to a boiler, allowing you to heat water and your vehicle with just one appliance. Both functions can also be used separately. Truma Combi heaters are suitable for both caravans and motor homes and have a water container with a capacity of ten litres.

Combination appliances usually run on gas, which means that they don’t need a power supply. Some models have integrated electric heating elements that allow water and the vehicle to be heated when the motor home is stationary at a campsite. Mixed gas and electric mode is then also possible. The diesel variants of the Combi heater are suitable only for motor homes, as they use diesel fuel from the vehicle’s tank.


  • Heating and hot water from just one appliance
  • Space-saving, as just one appliance is installed
  • Ten litre water capacity is sufficient for showering
  • Different models for different needs


  • Heater and water heater cannot be replaced individually

Tips: Cleaning water heaters

For hygienic reasons it is advisable to clean Boilers and Combi heaters regularly, especially after they have not been used for some time. Normal household vinegar essence or citric acid are suitable for decalcifying. Always pay attention to the manufacturer’s recommended mixing ratio on the package.

Clean AquaGo with special AquaGo decalcification tablets, which are available at specialist retailers.

For more detailed information see the operating instructions!

Lime scale occurs especially as a result of precipitation from "hard" water. The appliance must be decalcified regularly depending on water hardness and hot water consumption.

Only use AquaGo decalcification tablets to decalcify the appliance to avoid damage and the voiding of your warranty.

  • Never use vinegar.
  • The use of non-Truma-approved substances for decalcification can cause chemical reactions and produce hazardous substances that could enter the drinking water.

The Truma UltraRapid HWS must be descaled on a regular basis (at least twice a year).

We recommend the use of suitable normal commercial products for the cleaning, disinfection and care of the Truma UltraRapid HWS. Products containing chlorine are unsuitable.

In order to avoid the colonization of micro-organisms, heat up the Truma UltraRapid HWS to 70 °C at regular intervals.

The drain valve and the P&T safety valve are to be operated regularly to remove lime deposits and to ensure that they are not blocked. Frequency: every 6 month.

Use wine vinegar for de-scaling the water heater, this being introduced into the appliance via the water supply. Allow the product to react and then thoroughly flush out the appliance with plenty of fresh water. To sterilise the water we recommend "Certisil-Argento". Other products, particularly those containing chlorine are unsuitable.

To avoid infestation by micro-organisms, the boiler must be heated to 70 °C at regular intervals.

The drain valve must be actuated regularly (at least twice per year) in order to remove limescale deposits and to ensure that it is not blocked.

Biofilm, deposits and limescale must be removed using chemicals to protect the unit from infestation by microorganisms. Only chloride-free products must be used in order to prevent damage to the unit.

The effectiveness of the use of chemicals to combat microorganisms in the unit can be increased by heating the water in the hot water system to 70 °C at regular intervals.

  • Select "Gas" mode.
  • Set water temperature to 60 °C.
  • Switch on device.

Once the water in the hot water system has reached a temperature of 60 °C, the burner will switch off. The unit must stay switched on for at least 30 minutes and no warm water may be removed. The residual heat in the heat exchanger will heat the water up to 70 °C.

Tips: How to protect your water heater from frost

When temperatures are falling or if frost has been announced, you must drain AquaGo, Boilers, UltraRapid and Combi heaters completely. Any water remaining in the appliances could freeze and cause the water container to burst. Therefore, observe these tips

In frosty conditions there is a risk that water in pipes, taps and appliances could freeze. This can cause considerable damage.

  • Never operate the AquaGo basic in frosty conditions, this model must be winterised.
  • Winter operation will not protect the RV’s entire water system. Water lines, taps, water tanks and the external water valves and the vehicle must be heated separately.
  • The RV must be designed for winter use/freezing conditions.
  • The water pipes in the RV must be ice-free to operate the AquaGo comfort / AquaGo comfort plus in winter. Otherwise, there is no water flow and the appliance does not start.

For winter operation and winterising the appliance please see the operating instructions!

If the vehicle is not used during periods of frost, it is essential that the Truma UltraRapid HWS be emptied.

  • Disconnect power for water pump (main switch or pump switch).
  • Allow the appliance to cool down.
  • Open hot water taps in bathroom and kitchen.
  • Open drain valve. Lever in the “f” position (drain). The water heater is now drained directly to the outside via the drain valve (3).
  • Check that the water has been completely drained (14 litres).

If just the cold water system is being used, without water heater, the heater tank is also filled up with water. In order to avoid damage through frost, water must be drained by means of the drain valve, even if the heater has not been used. As an alternative, two shut-off valves, resistant to hot water, can be fitted in front of the cold and hot water connection.

Never operate the water heater without water in it!

If the motor home / caravan is not used during the winter, the hot water system must be drained.

  1. Switch off the power to the pump assembly (main switch or pump switch).
  2. Open hot water taps in kitchen and bathroom. In order to check the water that is flowing out, place an appropriate container (capacity 10 litres) beneath the drainage socket (d) of the drain valve.
  3. Open drain valve: Move lever to position (c) – vertical.
  4. The water from the hot water system drains through the drainage socket (d). The drainage socket (d) of the drain valve must be free of blockages (slush, ice, leaves, etc.) at all times so the water can drain easily!
  5. Check whether all of the water in the hot water system (10 litres) has been drained into the container via the drain valve.

The interior can be heated in gas, electrical or mixed mode, either with or without water, depending on the setting.

Truma water heaters at a glance

Product Area of use Energy sources Volume Heating element  Heating time 



1,3 L -

When the appliance is switched on, 

the burner starts automatically as 

soon as the hot water tap is greater 

than approximately 1.5 litres per 

minute. Standard water outlet 

temperature: 49°C

UltraRapid Gas


Gas 14 L -

approx. 20 °C to approx. 65 °C:

approx. 45 min..

UltraRapid Gas / 


​ ​ 
Gas/electricity 14 L 1415 W

approx. 20 °C to approx. 65 °C:
approx. 28 min. (mixed mode)
approx. 40 min. (electric mode)
approx. 45 min. (gas mode)

Boiler electric

Electricity 14 L 850 W

approx. 15 °C to approx. 70 °C:
approx. 70 min.

Combi 2 E

Gas/electricity  10 L 980 W / 1960 W

approx. 15 °C to approx. 60 °C:
approx. 20 min. (water container only)

Combi 4 E


10 L

980 W / 1960 W

approx. 15 °C to approx. 60 °C:
approx. 20 min. (water container only)

Combi D 6

Diesel 10 L -

approx. 15 °C to approx. 60 °C:
approx. 20 min. (water container only)