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Eberspacher Heater FAQ's

The heater switches on and only operates for 20 to 45 seconds and then stops.

This is the classic symptom of low voltage to the heater under load, so please check the voltage at the heater power input connection with a multi-meter when you initially switch your heater on. See point numbers 1 to 4.

1. Check the battery battery voltage going to your heater. It should be: 10.5V to 14V (12V system) or 21V to 30V (24V system) under load.

Many heaters have failed to operate because the battery voltage has become too low due to lack of battery charging or excessive power drain from other ancillary equipment or faulty batteries.

2. Check the wiring harness or connections for corrosion, the build up of corrosion around a terminal or battery connection will hamper the connection or the batteries ability to allow power to pass. Whilst checking the condition of a terminal, don't forget to check the terminal or connections security.

A loose terminal or connection can have the same affect as corrosion.

Maybe cleaning and applying some corrosion inhibitor (e.g. petroleum jelly) will prevent this problem from occurring again in the future. A routine check of all terminals and connections is always a good method of preventative maintenance with any vessel or vehicle.

3. Check the condition and rating of the fuses used on the heater ensure they are in good order and the correct amperage. As stated in 1.2 above, corrosion and loose connections can cause problems.

4. Undertake a visual inspection of the heater and its associated parts. Is there any physical damage to any component parts as this may have a detrimental effect on the heater's ability to function correctly?

The heater does not work.

Is there any power to the operating unit (e.g. lights or display digits) Check if a fuse has blown, refer to the technical manual for your heater that the correct amperage fuse and type has been used. If you replace the fuse, ensure the correct amperage is fitted. Should the fuse still "blow" then you must contact you local Eberspacher distributor for further assistance.

Do not under any circumstances increase the amperage of the fuse in an attempt to cure the problem. The correctly rated fuse is there to protect the heater and the wiring in the event of an electrical short circuit.

Remove the ignition glow plug and check coils for continuity or excessive build up of carbon across the coils.

The heater fails to fire up after trying for three minutes.

Conduct a visual inspection of the intake to the heater, the warm air ducting and the air outlets. A restriction to the airflow can make the heater overheat.

Has the ducting been crushed, the air intake to the heater inhibited, or have any or all of the outlets been closed off.

Check that the airflow into and away from the heater through the ducting system is not restricted.

For water heating systems, check that there is adequate water flow around the piped system. Ensure that regulating valves are open and functioning correctly. Ensure that no air is trapped within the heater emitters, i.e. the radiators, fan matrices or fin radiators. Bleed the air from the system if necessary.

Important: when topping up the header tank, us a 50/50 mixture of antifreeze to water solution.


Check the heater exhaust pipe and combustion air tube for any damage or possible restriction. Water ingress in either tube or any mechanical damage can influence the operation of the heater. Please check this out.

The heater fires up, runs for a short period and then shuts down again.

The heaters are fuel fired units, so a lack of fuel could be the reason why the heater is not operating as required. Within the heater's fuel line system is a "Fuel metering pump" that contains an internal fuel filter. Refer to the technical for location of the filter.

This small pot shaped filter may need cleaning or replacing. A blocked or restricted filter will not allow the heater to run efficiently and maximise the potential heat energy available. Should the boat or vehicle be subjected to rough weather or travel over rough ground, sediment in the bottom of the tank may have become disturbed and is now blocking the metering pump filter. So please check this out.

This problem usually revolves around lack of fuel being delivered into the combustion chamber. It always worth checking out the comments made in Q3 for air and water heaters. Your heater may be overheating.

It could also be the thermostat or modulator is set too low, ensure that the thermostat or modulator control is adjusted up to a higher setting.

Check that the fuel metering pump is working, this is confirmed if the fuel metering pump is "ticking" also check that fuel is being delivered to the heater fuel inlet connection, and check all fuel line joints for security and that they are not either leaking fuel or allowing air into the fuel system.

Check the fuel level gauge, have you run to low on fuel in the main fuel tank?

Check that any heater fuel shut off valve is in the open position.

Inspect the exhaust pipe or combustion air tube for any restrictions.

When the heater is switched on the blower motor runs very slowly but the heater does not fire up.

A fault has been detected by the control box during the pre-start diagnostic phase. In this instance you will need to contact your local Eberspacher dealership, who has the necessary diagnostic equipment to determine the actual reason for the heater not operating.

The same situation would also apply to Hydronic water heaters.Q6: I have just purchased a second hand heater, which I would like to change over the operating voltage? i.e. from 12V DC to 24V DC or 24V DC to 12V DC.

I have just purchased a second hand heater. Can I change the operating voltage? (12V to 24V DC or 24V to 12V DC).

It is not economical to change over the voltage of the heater as this will entail the following changes.

The control box, fuel metering pump, blower motor, voltage regulation relay and in some case the ignition system will have to be modified.

Will my Eberspacher heater run on red diesel and how often will it need servicing?

"Our heater products are designed to run on fuel to specification BS EN 590 as stated in the Technical book that accompanies all heaters".

It is commonly thought that red diesel is road diesel with a red dye in it. Unfortunately, this is not always the case. There are two types of red diesel available, one is Gas Oil with red dye, and the other is Low Sulphur Gas Oil (City Gas Oil) with a red dye. The latter meets BS EN 590 and has the same specification as road diesel.

We have contacted a couple of Fuel Suppliers to ascertain "what exactly is it in the fuel that makes it different".

The main differences between "Gas Oil (non BS EN 590)" and Low Sulphur Gas Oil (to BS EN 590), is the former has a lower 'Cetane rating' 46 against 52, higher sulphur %Wt 0.2 against 0.005, higher Flash point 82 against 67 and Carbon residue, on 10% distillation residue, %Wt .12 against <0.001.

The fuel commonly found on the canal system is unfortunately "Gas Oil". The other "Red diesel" available is called "City Gas Oil" (ultra low sulphur gas oil) (Linton Fuel Oil Ltd Stock code 103). This meets BS EN 590 and apparently costs the marina only 1.5 pence more per litre. Our contact was quoted saying "why anyone chooses to buy normal gas oil, I don't know!" another supplier was challenged to why it was not always offered he said "surprisingly no one asks for it but it is readily available".

We have found boat owners using the better quality fuel to have a longer period between servicing, therefore what is needed are people like you demanding this far superior fuel. I am sure you would be happy to pay a few pence more for better fuel.

In answer to your servicing questions our heaters have a service interval of approximately 2000 hrs, this can be adversely affected by the use of Gas Oil (non BS EN 590), bacterial or water contamination. We have many customers who have taken onboard the advice we have given in the past regarding additives and now have far longer service intervals. Additives such as 'Fultron' are available from all good chandlers and stockists.

Webasto Heater FAQ's

What are the main advantages of heating with diesel?

Fuel autonomy: Diesel fuel is uniform worldwide and available 24/7, all year long. A very precise monitoring of fuel supplies is possible via the fuel-gauge.

Heating autonomy: Heating while driving is allowed worldwide. By supplying the heater with diesel out of the vehicle fuel tank, there is no need to search for fitting bottle connectors or hassle of exchanging gas bottles in foreign countries.

More space: Gas bottles in motorhome can be reduced as they will last longer and all Webasto heaters can be mounted outside the vehicle. This leads to significantly more space inside the motorhome.

Less weight: In winter, more than 80% of LPG gas is needed only for interior heating. By using diesel operated heaters, the LPG gas bottles can be downsized to one single 5 kg bottle. This means that up to 35 kg of additional load can be gained.

Can we sleep in peace with diesel heaters?

The technology of diesel heaters has experienced huge innovations since the first heaters were introduced. Together with specially configured motorhome heaters, Webasto provides silent application kits whose various accessories eliminate all possible disturbances (i.e. exhaust silencer, ultra-silent pump, etc). This ensures your comfort and the comfort of your campground neighbour.

Is it necessary to equip Webasto heaters with a catalyzer?

No! Webasto heaters do not need a catalyzer thanks to the very effective burning process. The exhaust values of our heaters are already on a very low level within the legal requirements.

Can Webasto heaters be operated while driving?

Yes! Heating while driving is allowed worldwide for all our heaters! This way you can have a cosy and warm interior already when arriving at your holiday destination.

Do Webasto heaters work in high altitudes?

Yes! All Webasto heaters are tested and approved to work reliably up to 1,500m which is sufficient for most European mountains. The Air Top Evo and Dual Top Evo range even work up to 2.200m thanks to the integrated automatic altitude sensor. On request, the Air Top 2000 ST is equipped with an integrated switch for altitude operation of up to 2,200m.

For altitudes above 2,200m it is possible to adjust Webasto heaters. Please contact your local Webasto dealer for further details.

Passing over the mountains while the heater is in operation, is not a problem for any of the Webasto heaters.

How can I make sure that the heater works in very cold climates?

All Webasto heaters are tested and approved to work in a temperature range from -30° to +40°C or more. The fuel used in very cold climates, where temperatures can fall considerably under 0°C (arctic diesel or winter diesel), is automatically mixed with additives to prevent freezing of the fuel. By using this fuel it ensures that no special preparation of the heater is needed. Basically, if your vehicle can drive, your heater will run as well.

Can Webasto heaters be operated with biodiesel?

All Webasto heaters are tested and approved to work with the legally permitted biodiesel content. The usage of a higher content of biodiesel however will reduce the lifetime of the heater.

Do Webasto heaters need to be serviced? Is a regular technical inspection needed?

Generally no! Webasto heaters are maintenance-free and do not have to be inspected every two years. We do recommend that you should operate your heater every two months for 10-15min.

Can Webasto heaters be retrofitted?

Yes! Webasto offers retrofit kits for all heaters. The kits contain everything that is needed to get the heater running. Only vehicle specific air ducting, mounting and fuel parts need to be added. Get in touch with our trained dealer network and ask for a bespoke quotation to retrofit a Webasto heater into your motorhome. Even if you are equipped with a LPG gas heating system it may be wise to have a redundant diesel heating system which provides faster heat, with more power.

What is the use of an additional heater?

There are different possibilities when it comes to additional heaters: Large (e.g. integrated) motorhomes usually loose the majority of heating energy through the windscreen. The big windscreens are not well isolated and condensation concentrates in this area. Also, if you turn the drivers and passenger seats to the dinette you may feel cool air on your back.

In order to avoid both, the Thermo Top C Motorcaravan heats the driving cab and reduces the condensation accumulations. It is mounted into the engine compartment and the air is distributed through the vehicles own fan system.

An additional air heater can be utilised when your existing heating system is not sufficient or perhaps you'd like to feel more secure on holiday by not having to rely on your LPG gas supplies. You can use the larger Webasto heaters to either heat the entire motorhome. You can also use the Air Top 2000 ST when a bit more power in the front area is required or to warm other parts which are not well reached by the existing main heater.

Can I install a Webasto heater myself?

The Webasto heaters need to be installed by an authorized dealer. Otherwise any warranty or liability for damages or repairs may be refused

Where can Webasto heaters be mounted?

Webasto heaters are designed to be mounted outside the vehicle ensuring more valuable space inside.

Air Top & Dual Top heaters can be mounted under the floor, into the doublefloor of the motorhome or inside the cabin. The Air Tops can even be tilted up to 90° if necessary.

Thermo Top C heaters are usually mounted in the engine compartment or under the motorhome.

Is a technical inspection of the motorhome necessary after the installation of a Webasto heater?

No! Thanks to the E1-approval, which is granted to all Webasto heaters, it is not necessary to make any technical inspection or registry in the motorhome registration documents.

How do Webasto heaters get supplied with fuel?

Each heater has its own fuel system with a dosing pump which takes the fuel directly and independently out of the vehicle fuel tank.

How much fuel does a Webasto heater need per hour?

Fuel consumption is strongly dependent on the heaters need for heating power and the type of heater. As a very rough and noncommittal guide, a heater needs 100ml diesel per hour. The heater only uses fuel when combustion is in process. For further details, please see the heater's technical specifications.

Does a Webasto heater empty the fuel tank when running?

No! The fuel connection of Webasto heaters uses the return pipe or a separate fuel tank extractor. The suction hose will not reach the fuel tank ground so that a reserve in the fuel tank is always secured.

How much electricity does a Webasto heater need per hour?

The electrical consumption depends on the heating power needed and the type of heater. The Air Top 2000 ST, for example, needs only 14 to 29W. To maintain the temperature once set point is reached, the electrical consumption is at the lower level. With these low electrical consumptions, you can rest peacefully knowing that you do not have to worry about your heating autonomy. For further details, please see the heater's technical specifications.

Does a Webasto heater empty the motorhome battery when running?

No! Webasto heaters are equipped with an under voltage protection so they will shut down before the battery conditions become critical. This ensures that the engine will still start. Motorhome heaters are usually connected to a secondary battery which does not have any impact on the engine start.

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