I have an aux heater fitted but have never seen it work. How can I manually start it up to check it?

Others may have a technical fix to answer your question (I think there is a kit available from Webasto for testing it but at a price and also I think the IID tool will test it) during the summer months you will not get it firing up automatically as it needs a temperature of 5C or less as you will have read.

However I had an accessory fitted so that if I use my key fob to turn on the headlights for 5 or six seconds and then turned them off again (whilst still in the house having my morning cuppa) the Fuel Burning Heater would fire up and run for about half an hour warming the coolant in the engine. This is designed to make starting easier and also reduce excessive fuel consumption which can occur when first driving a cold diesel engine. It also means that the interior heater gets warm air to the cabin quicker once the engine has been started. Whilst the FBH is running and without the engine being started, you will be able to hear it working (a roaring noise) and sometimes see the white exhaust gases from the nearside front of the car. Robin
2008 Range Rover Sport TDV8
Gone:
Jaguar S-Type V8 4.2 Sport
MGZTT 190 2.5

If you have a look on the disco3 forum there is a good write up by a gentleman called Robbie.