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Caravan Systems

How the 12v, gas and electric systems work Caravan Systems.

There are four different systems in a caravan which all integrate with each other in different ways: 

  •  The water system.

  •  The 12v electric system

  •  The 240v electric system

  •  The gas system 

The Water System.

This incorporates the water pump, water heater, filters, pipes, taps and toilets.

Operation: The 12v system (battery) has to be connected with the pump switch on and the pump located in the water inlet.

A 12v water pump is used to transport the water through the system, through the water heater and up to the taps. There are two types of pump, a submersible, which is placed directly into a water container and an inline, which is self-priming. Both pumps operate when a tap is opened, completing a 12v circuit, either by a micro switch in the tap or a pressure switch in the pipeline.

Water filters are fitted into some systems, which need changing periodically, refer to manufactures guidelines for details.

Water Heating

The  water is heated using a 240v element or a gas burner. The water heaters in modern caravans are storage heaters so it is important to insure the water tank is full before it is turned on, this is done by running the hot tap until a full flow of water appears. The water is heated and normally takes 30 minutes to reach full temperature.


Cassette Toilets 

Most models of cassette toilets have their own water tank and pump. The water tank is filled up externally; the pump can be manual or 12v. However some newer models of toilet use the submersible caravan pump to flush.

The water system needs to be drained in winter to prevent frost damage, see Drain Down.


12v Electric system

The 12v electric system runs the 12v strip/spot lights, water pumps for the main water system and the cassette toilet. 12v’s are also needed to run appliances such as the gas side of the water heater, fan master heating system and some fridge/cooker ignition systems.

Connection: A 12v battery MUST be fitted to the caravan to supply the 12v electric system. With a battery in good condition all the above items will work correctly.

The gas side of the water heater needs a 12v feed to operate the solenoid and spark generator, without 12v’s it will not work.

The 240v fan master/ultraheat heating system needs 12v’s to operate the fan that circulates the warm air around the caravan, without the fan working correctly the fan master will over heat and trip out.

Newer Truma Ultraheat heating systems and the Carver 4000 240v heating systems do not need a 12v fan for them to run correctly.However it is recommended to use the 12v fan when the 2000 W setting is selected to avoid heat build up at the rear of the unit.

If a battery is not fitted, damaged or the fuse has blown therefore taking it out of the circuit, the charger will supply the 12v system.

You may not notice this happening as everything will work as it should.

The main issue in this instance will be that the charging system may give up to 17v, this will do long term and costly damage to volt sensitive circuits such as the water heater and space heater, if fitted with a fan.

The battery system should be checked periodically. To do this, ensure the battery is connected to the caravan, remove the 240v connection. This will stop the charger from working therefore test the battery system.

Test the 12v’s by turning on a strip light; if the 12v’s run ok the 240v can be reconnected.


Gas System 

The gas supplies the cooker/hob, space heater and water heater.

The gas bottles are stored in an outside locker and are connected to the caravan via a regulator. There are two types of gas, Propane and Butane.

The main difference is that Propane has a lower freezing point which allows it to be used in freezing conditions such as are found at the beginning and end of the season.

When the caravan is in use it is safe to leave the gas turned on.

When the van is left for a long period of time, in storage or being towed the gas bottles should be turned off or removed.

If the shower is being used frequently then the gas can be put used to keep up with the demand for hot water.

Both gas and 240v can be used at the same time.

Due to the propities of gas it is highly recommended that the system should be checked on an annual basis by a professional.

Ventilation requirements are built into the caravan at manufacture; purpose built vents should NOT be blocked to stop draughts. The water heater and space heater are both room sealed units, this means the products of combustion never enter the living space making them very safe to use.

You may find that the gas oven isn’t as efficient as a household appliance; allowances will have to be made to cooking times. 

Appliance operation 

Most gas appliances with manual ignition, i.e. cooker, space heater, fridge will have a knob or dial that has to be depressed to allow the gas through. The burner can then be lit using a built in sparker or gas match.

The knob then has to be kept depressed for 10- 20 seconds to allow the thermocouple to operate. Once the knob is released, the flame will stay lit. 



The 240v system is perhaps the system you will get the most use out of. It runs the fridge, water heater, space heater, transformer and sockets.

The 240v is plugged in to the outside of the caravan; in most modern caravans the socket is located in the battery box.

Once it has been plugged in the system will then become live.

The refrigerator has a switch located on the front panel, normally a rocker switch which the 240v can be selected from or a green illumated switch.  Under normal conditions the fridge will be cool within an hour.

The 240v system in a caravan has its limitations. The box that you plug into will be rated at a maximum of 16 amps. This means that you have a limited amount of power that you can use before it will trip out.

The guide is 2000w(2kw)max. A household kettle or toaster is around 2kw, this may trip out the box if used depending on what other systems are on in the caravan and the sensitivity of the box.

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