Jungle,
Ok i don't have the optional timer programmer thing so I'm struggling with that side of things.
This could be one of many things and, as with all electrical gremlins, time consuming to fix.
If your fan runs but no heat I'm going to suggest it's either fuel (as Dan pointed out) or glow plug (assuming diesel). I don't think the fuel pump runs untill about 30 seconds into the cycle?
So, switch the heater unit on and crawl under the van. On the side of the heater (sliding door side) you'll see the pump and the glow plug at a jaunty angle sticking out of the heater body. There should be a rubber condom over the top of it. Pull this back and stick your pinky on the tip of it. If it's functioning you'll feel the heat ! If not, there is your problem. From there you'll need to get the volt meter out to determine if the plug is dead or simply not getting a supply.
Disconect the cable and check the voltage to earth.
Assuming the plug is hot the next thing to try is to give the fuel pump a sharp tap. They're facet type pumps and can get a bit sticky. A sharp tap usually clears them. Operation is a pulse, approx one/second. You'll hear it clicking away. If it is working, try pulling of the pipe to the heater unit to ensure there is fuel flow. You'll need to maintain the slightly upward angle, supply being lower than output. If there is no fuel flow take the pump off and blow through the pipes. Check you have fuel in the main tank to a decent level as the system is designed to not empty the main tank.
If non of these things work then we need to get the wiring diagram out and start checking some stuff from the harness connection behind the main cupboard. It's easy to get to and straight forward.
I won't go into it here but will be happy to once you've checked out the above.
One other possibility, the little control panel where you switch the unit on/off from can suffer from dry solder joints.
Inside are two pcb's set at right angles to each other and linked by a series of bent solid wires soldered at each end. These joints can become dry and problematic. I resoldered all of mine and it cured several problems.
Let us know.
I've tried to move this post to the T4 section so if it vanishes we're over on the "light side"
S.