2004 van, this is pre upgraded control board for the ultraheat and pre fitting the temperature stat in a sensible place, either or both of these could be having an effect on your electric heating.
Apart from the stat not responding to temperature change as it should, a common problem with older control boards is lack of 2kw heating due to a faulty relay not switching it on.
Understanding the system might help determine if it's user error or a fault with the system, I wrote this as my thoughts on how blown air heating works;
Blown Air Heating
All but the smallest caravans are fitted with a gas fire rated at 3.5kw output and almost an equal number of vans now have mains electric heating rated at 2kw output and giving a total of 5.5kw. This heating is generally distributed around the van by the hot air being blown along ducting and hence the name.
It is often said this system of blowing the air around the van is not as good as without, or at least until the heater itself as got hot, well this is simply wrong
When you get to site the van is stone cold, not just the air inside but the vans whole fabric, that's the walls, furniture, cushions, everything. So when the fires switched on it's got a big job to do, it will only take a few minutes to warm the air but this heat will be absorbed by the fabric just as quickly. Depending then on how cold it all starts will determine how long this process takes and the whole van comes up to a comfortable temperature.
1), So how do you get it there as quickly as possible? there is only so much heat available from the gas fire and or the electric, so as both can be used together this is the best thing to do. In this situation though the fire may well overheat, it is therefore essential to use the fan to move that heat quickly.
2), While this process goes on the air returning too the heater will be slightly cooler than the overall temperature of the van which at the beginning will feel to 'us' somewhat colder still. However the heaters themselves get to full temperature in under 5 minutes, blown air on or no.
3), Without the fan, hot air from the heaters will rise straight to the roof where there are one or two roof lights with fixed ventilation for it to go straight out. The hot air that does escape will be instantly replaced by outside stone cold air coming in through floor level ventilation.
3 and a half), With blown air on, hot air from the heater is forced down to floor level where most of the major fabric is, this then can now absorb the heat more quickly and also slows down heat wasted through ventilation as some of this blown air is used to heat up what cold air does come in.
So as much heat as possible and blown air straight away is best, but it must be remembered to give it enough time to heat everything to a desired temperature before turning back the heating too much.
At some point the fire will get on top of the job and can be turned down, if though you do this to quickly and the fabric is still absorbing a lot of heat, then the overall temperature will drop to low as the heater is unable to replace heat fast enough, the van will always then feel 'draughty' In this case it's no good turning up the temperature setting as the heaters already on, you need to increase the total heat output.
Once though an equilibrium point is reached and the van is fully warm, all the heater needs to do is heat air coming in through normal ventilation and quite low heat settings can often maintain a constant temperature
If now a door is opened, a rush of cold air is quickly warmed by taking heat from the fabric which in turn gives the heater chance to replenish that heat loss without you probably noticing for more than a few moments.
With that in mind, if you do feel a slight dropping off of the overall temperature, it is wise to turn the heating up slightly straight away rather than letting the van cool off to far and your left in the cold waiting for it to heat up again.
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