Hello Jason,
Most caravans have two electrical power systems. The 12V dc circuit which powers things like the water pump, some of the internal lights (usually fluorescents), and the hot air circulating fan this is usually fed from a 12V battery. The battery is usually charged when you tow through the multi-way plugs that connect to the car, but it is also usually connected to a mains powered charger/power supply which only works when the caravan is plugged into a mains supply.
The second power system is the mains 230Vac. This is only available when the caravan is plugged in to an external mains supply. This powers the battery charger/power supply mentioned above, as well as the fridge, usually a water heater, and of course the mains sockets in the caravan. In your case it sounds as though you have space heater that can also be powered from the mains. There are usually some mains powered lights in the van.
The reason that some appliances do not use 12Vdc to power them is that they need a lot of power, and the 12V system cannot provide enough.
The items that are on the 12V circuit, tend to be those that you might need if you caravan on sites without mains hook ups, hence the water pump, and the hot air circulation fan. The mains appliances tend to be those items that might be considered nice but not essential -except of course, the fridge, water heater and the space heater.
For these appliances you usually have the option to use gas to power them. If it is a new caravan you should have details of each appliance in your caravan handbook. If you have not got the hand book, then either contact the caravan manufacture or look on Ebay or some contributors to this forum have various handbooks available.
If the Gas appliances have not been used for a long time, it would be wise to have then serviced.