Like your gas appliances, your diesel heater should serviced annually if you use it regularly, or every 24 to 36 months if not used regularly. Diesel heaters become very dirty inside the burner, the wiring connections can become corroded, the ducting and fan can get blocked up and among other things, this can cause the unit some very serious damage.
A Diesel Heater Service can include, depending on the model, replacing the glow pin, burner and motor gaskets and fuel filter, and a general clean. These prices can vary depending on your particular model.
Please contact me with details of your RV and the diesel heater model number so I can give you an over the phone quote.
There are a few things you can do to help prolong the life of your diesel heater.
Vacuum around the heater regularly, particularly removing any dust that will be sucked into the internal air intake of the heater.
Regularly inspect the external exhaust and air intake, look for the early construction of wasps nests etc, clean out any mud or dust.
I recommend running a 10% kerosene/diesel mix to help prevent diesel waxing and clogging the diesel filters, particularly in weather that is below 1 degree Celsius.
Every 6 to 12 months, run a rich mix of kerosene through the heater. Operating on 100% kerosene is fine (and recommended in alpine climates). Kerosene helps to clear out the carbon build-up, which is the main issue causing need for service.
Start it up and run it for half an hour each month. I also suggest this for your gas appliances as well. If the van is sitting unused, go out to the van, fire everything up, make a coffee and sit down and read the paper. If your van is sitting unused for long periods, this also helps keep you familiar with how to operate all the functions of your van, and you may discover some other maintenance needs prior to taking off on your next big trip.
There is a wealth of knowledge on this webpage; http://www.letonkinoisvarnish.uk/Fault_codes.html This link shows the fault codes for the Eberspacher heater which can be helpful in determining what is wrong with your heater in the event that it doesn't run. The page is a little hard to navigate, but all the information is there and very helpful if you decide to service your own heater.
Below is a few photos of the steps involved in dismantling a Planar heater for servicing (which is basically the same as Webasto)