How to Use the Truma Instant Hot Water System in Your Mars Caravan

The Truma instant hot water system fitted to selected Mars caravans is designed to give you continuous hot water on demand – no waiting for a tank to heat up and no running out mid-shower. This article explains the basics of how it works and how to use it safely in everyday camping.

1. What Is the Truma Instant Hot Water System?

Unlike a traditional storage hot water service, the Truma instant system (such as the Truma AquaGo range) is an instantaneous gas water heater. Instead of heating a large tank, it heats the water as it flows through the unit.

In simple terms:

• It is connected between your fresh water supply and the caravan’s hot water pipes.
• It runs on LPG gas with a small amount of 12 V power for the electronics and ignition.
• When you open a hot tap, a flow sensor detects water movement and the burner automatically ignites.
• The burner output is adjusted electronically to deliver a stable hot water temperature to your tap or shower.

The result is effectively “endless” hot water within the unit’s design limits – as long as you have gas, water and 12 V power.

2. Key Features (Plain-English Overview)

• Instant and continuous: Heats water as you use it, so you’re not waiting for a tank to recover.
• Constant temperature: The system adjusts the flame to keep outlet temperature around a set point, reducing sudden hot/cold bursts when someone turns a tap on or off.
• Gas-only heating: Uses LPG for heating, so you can have hot water even when you’re off-grid (you still need 12 V power for control electronics and ignition).
• Smart controls: A simple control switch or dial inside the van allows you to turn the system on/off and, depending on model, select modes such as Comfort or Eco.
• Service-friendly design: The unit is mounted externally behind an access door so it can be serviced by a licensed gas fitter or authorised service agent.

Exact features and control layout can vary slightly between Truma models and Mars caravan layouts, so always refer to your van’s specific user manual for detailed information.

3. Before You Use the System

Each time before relying on hot water, quickly check the basics:

• Gas supply: At least one gas bottle is turned on and has gas available.
• 12 V power: Your caravan’s 12 V system and any relevant water heater fuse/isolator are switched on.
• Water supply: You have water in the tanks and/or are connected to mains water, and the pump is on if needed.
• Exhaust and intake: The external Truma hot water access door is not blocked by chairs, covers, walls, snow, mud or anything else that could restrict airflow.
• No DIY work: Do not remove covers, adjust gas components or attempt internal repairs yourself – all gas work must be done by a licensed gas fitter.

4. How to Turn the Truma Instant Hot Water System On

Your exact control switch may vary slightly by model, but these are the general steps used in most Truma instant installations:

1. Ensure 12 V and gas are available
   Turn on the caravan’s 12 V master switch and make sure at least one gas bottle is open.
2. Locate the Truma control switch or panel
   Inside the van (often near the main control area or ensuite) you’ll find a Truma water heater switch or small control panel. This may be a simple on/off selector or a rotary switch with modes such as OFF, ECO and COMFORT.
3. Select the desired mode
   
   Turn the control from OFF to your preferred heating mode:
   • ECO: Energy-efficient mode that typically gives slightly slower response but reduced gas use.
   • COMFORT: Faster response and more stable hot water temperature, ideal when you’re using the shower or doing multiple tasks with hot water.
4. Wait a few moments
   The unit will power up and be ready to ignite when it senses water flow. You may not hear anything yet – that’s normal.

Once the system is “ON” and in a mode, it will automatically start the burner when you open a hot tap and stop it after you close the tap and the cool-down period has finished.

5. Getting Hot Water at the Tap or Shower

1. Open a hot tap or shower mixer
   Turn on the hot side (or set your mixer to warm/hot). After a brief delay, you should hear the heater ignite and feel the water begin to warm.
2. Let it run for a short time
   Because the system and pipework start cold, let the water run for a few seconds until it reaches a steady temperature. This flushes through cold water already in the lines.
3. Fine-tune at the mixer
   Once the heater is running, adjust your shower or tap mainly with the cold side to avoid confusing the temperature control. Large changes in hot flow can cause fluctuations, so small adjustments are best.
4. Turn taps off normally
   When you close the tap, the heater will shut down automatically after a short cool-down. You do not need to switch the main control off between each use.

If the water temperature suddenly changes when someone else uses water (e.g. another tap or the toilet), adjust the mixer slightly or wait a moment for the system to stabilise.

6. Turning the System Off

If you won’t be using hot water for a while (for example, overnight or when travelling), you can switch the system off:

1. Ensure all hot taps are closed and no one is in the shower.
2. Turn the Truma control back to OFF.
3. If you are packing up or storing the van, turn off the gas bottles and 12 V master as usual.

Do not turn off the 12 V supply while the burner is operating or cooling down – always allow the heater to shut itself down after you close the tap.

7. Basic Do’s and Don’ts

Do:

• Run the system in COMFORT mode when you’re showering or doing multiple hot water tasks.
• Allow a few seconds for hot water to reach the tap each time.
• Keep the external vent area clear of obstructions.
• Have the system inspected/serviced by a licensed technician in line with Truma and Mars recommendations.

Don’t:

• Attempt to open the appliance casing, adjust gas components or repair the unit yourself.
• Block the exhaust or intake (e.g. with storage boxes, covers or annex walls pressed tightly against the vent).
• Use tools or high pressure on the access door; it should only be opened by authorised service personnel.
• Ignore persistent error lights or repeated burner failures – contact support instead.

8. When to Contact Support

Stop using the system and contact Mars support or an authorised Truma service agent if you notice:

• Repeated failure to ignite or frequent error indications on the control.
• Unusual noises, strong gas smell, or visible damage around the access door.
• Very hot/very cold swings that don’t respond to normal use or control changes.
• Water leaks around the hot water unit or from the access door area.

When you lodge a support request, please include:

• Your Mars caravan model and VIN.
• Confirmation that you have gas, water and 12 V power available.
• A description of what you were doing when the problem occurred (showering, washing dishes, etc.).
• Photos of the Truma access door and, if visible, any status lights or labels.

Summary

The Truma instant hot water system in your Mars caravan gives you on-demand hot water for showers and everyday use, as long as you have gas, water and 12 V power. Turn the system on at the Truma control, run the hot tap until the temperature stabilises, and let the unit manage the heating in the background. Use it within its design limits, keep vents clear and leave any servicing or gas work to qualified technicians so you can enjoy safe, reliable hot water on every adventure.