Periodic maintenance is vital for ongoing diesel heater efficiency

Servicing your diesel heater

A diesel heater is one of the greatest ways to keep your van toasty when touring during the cooler months. Unlike reverse-cycle air-conditioning, you don’t need to be hooked up to 240V mains power or running a generator. A diesel heater is great for free camping because all you need is a small amount of 12V power to run the fan and pump and, of course, the diesel fuel. It is a very efficient heating system.

A diesel heater is not maintenance-free, though; carbon deposits will form in the combustion chamber and reduce heating performance. The way to minimise this is to ensure the heater is run at full heat for a good hour or so to burn off the deposits and, in fact, to generally avoid running the heater on a low setting for long periods. A diesel heater should not be run for short periods either, as this will increase carbon deposits.

Periodic maintenance is vital for ongoing diesel heater efficiency. The key elements of a diesel heater service are to clean or replace the glow pin and to remove any carbon deposits from the combustion chamber, replacing it if necessary. The fuel filter should also be replaced, and fuel and exhaust lines checked. You can purchase a service kit for the job which comprises a new glow pin, a combustion chamber and gaskets. How often should this be done? That depends on how the heater is used and what quality of fuel is used. Between six-monthly to two-yearly intervals appears to be the range.


The heater unit firstly needs to be removed from the RV (in this case, we’re servicing a motorhome diesel heater but the principle is generally the same). The unit is very light, weighing just a few kilograms, and is quite compact. Usually installed in a cupboard or in an under-bed or under-seat storage area, generally speaking, the unit should be easy to get at.

There are a few elements to diesel heater unit removal: first the wiring for the fan operation and the hot air ducting outlet must be disconnected from above, then the connections for the fuel inlet pipe, combustion air inlet and exhaust outlet disconnected from underneath the van. Then, of course, the plates securing the unit to the van have to be removed.

The wiring harness for the heater unit is, in this instance, concealed under a plastic cover on the top of the unit. Unclipping the cover and disconnecting the harness completes this part of the job. Then disconnect the hot air ducting.

Then, from underneath, the plumbing has to be removed from the heater unit. This can be very easy or extremely difficult, depending on location of the installation and how long the connections have been exposed to the elements. In this case, access was very tight and that made it quite difficult to get to the securing clamps. Pipes can degrade and become difficult to remove from the connection points at the heater unit and the clamps can corrode or become impregnated with dirt and debris, also making for a less-than-straightforward removal process. Remove the bracket under the unit first, then disconnect the pipes and undo the nuts securing the unit to the mounting plate.

With the heater unit on a suitable work bench – clean and well-lit – the unit can be disassembled. The plastic outer casing is removed first, in this case with two black plastic end caps unscrewed. Then the grey halves can be separated and removed from the unit. The fan impeller is then unclipped from the motor shaft.

Then the upper body is unbolted from the heat exchanger unit. The combustion chamber (with glow pin attached) can then be removed and inspected. In this case, both the combustion chamber and the inner area of the heat exchanger unit had a large amount of carbon deposits evident, which would have certainly diminished heating capacity.

The carbon deposits can now be scraped out and the combustion chamber unit and the heat exchanger unit can be cleaned thoroughly in a parts washer or similar. Be aware that the carbon deposits are very messy and the fine particles get everywhere. Make sure you dispose of the deposits in the appropriate manner.

Now the glow pin can be removed from the combustion chamber unit and the new glow pin fitted.

The unit can now be re-assembled, ensuring the mating surfaces are clean with no old gasket material remaining on them. Fit the new gaskets and re-assemble the unit in reverse of disassembly.

If you don’t have an inline fuel filter, now is a good time to install one. Some people also like to fit a filter to the fan air inlet to avoid dust build-up in the unit, although this can cause more problems if the filter is too restrictive to begin with or is not checked regularly for blockages.

Be careful when re-fitting the unit to your van. While the securing plate is in situ you want to be sure the heater unit is sealed properly against its base and the connections for air, fuel and exhaust are tight and have no leaks.

While diesel fuel is not as flammable as other fuels, you do not want to risk a fuel leak. The same applies to the exhaust – carbon monoxide is odourless and if it leaks into the caravan you are putting yourself and your loved ones in danger. If you have any doubts about your mechanical ability, do not attempt this job – best leave it to the experts.

The full feature appeared in Caravan World #541 September 2015. Subscribe today for the latest caravan reviews and news every month!