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Eberspacher Diesel Water Heater Introduction

The majority of our Eberspacher pages are based on air heater models.

The fundamental difference between air heaters and water heaters is simply the way the heat is transferred out of the Eberspacher. Hence most of the general air heater information also applies to water heaters and that information will not be duplicated in water pages. I am now adding Eberspacher water heater pages but as we do not use water heaters ourselves my practical knowledge of these models is limited.

Please help improve the water pages by feeding back useful information.

I welcome corrections, constructive criticism, additions, photographs and especially donated heaters / parts.


You use any information and advice I give entirely at your own risk. If you do not accept this do not use this site, go to an Eberspacher dealer. I have tried to make it as accurate as I can but accept no liability for errors or problems caused by following our pages. Some of the information is only suitable for people with a good aptitude for mechanical and electrical repairs. Any DIY involves some risk of accidents and you must decide if you are capable and can do it safely before carrying out any work. You should also ensure your DIY is done to a professional standard in order to avoid creating potential hazards and insurance invalidation. Boat installations must strictly comply with Marine regulations.

Hydronic water heater operation

Hot water path

Water inlet

Heat exchanger outer

Heated water outlet

Combustion air path

Combustion air inlet

Combustion air impeller

Glow pin and screen

Combustion chamber

Heat exchanger inner


Right  Fuel inlet to pump.

Conventional home central heating systems have a single pipe from the header tank to the piping as shown on the right. This allows for expansion of the water and to top up small losses of water. Eberspacher water heaters generally use two pipes as in the arrangement on the left where the hot water flows through the header tank.This increases the thermal capacity of the system which reduces the number of times the heater drops into standby. Two pipe header tanks installations as shown are preferred for 4 and 5kw heater models. On larger heaters routing the main return via the tank is too restrictive on flow rate and it is usual to fit with a heater matrix or radiator return going through the header tank.

Model names

Eberspacher model naming is confusing so a brief explanation of the models may help. However we are still finding out about water heater models and there are some models may not be included.

Older models had a naming convention, newer models do not follow this system.

First Letter - D diesel, B petrol. Number generally represents heat output, higher number higher output

Letter - L air,  W water.  Older models only, newer models do not use this convention and use L for Large.

Any letters following identify the model, eg D1L,  D1LC,  D1LCC.

Water heater models

Oldest models             D4W (not sold in UK), D5W, D7W, D9W, D10W.

Hydronic OEM             D3WZ, D5WZ, possibly D4WZ   (OEM specific heaters with no water pump)

Hydronic current           D4WS (24v), D4WSC (12v), D5WS (24v), D5WSC (12v)

Hydronic M I                 D10W

Hydronic M II (2013)   M8, M10, M12,

Hydronic L I                 L16, L24, L30, L35

Hydronic L II                LII16, LII24, LII30, LII35

Manuals and servicing information that may be of interest

Download links for manuals

http://www.eberspacher.com/  and   http://www.espar.com/   used to have lots of manuals for downloading but recently the sites have been updated. Most manuals are no longer available from them.

Many manuals are still available from http://butlertechnik.com/      Otherwise contact us for copies.

Each model usually has an Installation manual and a Troubleshooting manual. Some also have a Parts list.

Eberspacher have replaced paper manuals with cd copies.

Servicing information water heaters

See our servicing pages.

For models not covered some of the manuals have Troubleshooting / repair manuals.

Feedback on our Eberspacher pages has been very positive, keep it coming.

As a result of the feedback I am still working on improving the existing pages, increasing the models covered as well as preparing extra pages.

If you want to add links to us from forum articles etc please do so, each link helps the site get more widely known.

I would appreciate an email if you found these articles useful. It helps me to gauge how much interest there is in particular areas and whether it is worth spending a lot of time improving the pages.

The reason for having this site is to promote our Le Tonkinois natural varnish and Flexidisc sander products, we hope you will look at those pages as well as these.

Fuel is pumped in tiny measured amounts into the Eberspacher. It is mixed with the combustion air and burnt in the combustion chamber, the hot gasses pass through the inside of the heat exchanger before reaching the exhaust.

Water flows through the heater and is heated as it passes over the outside of the heat exchanger.

Eberspacher video  http://www.espar.com/videos/hydronic-tech-info.html is informative, you can skip over the first minute.over the first minute.

The target temperature of the heated water is fixed by the ECU inside the heater and not adjustable.

The system should be filled with a 10% to 50% antifreeze mixture, this also gives anti corrosion protection. Eberspacher stress the importance of fitting correctly adjusted balancing valves especially in the calorifier feed. They also recommend operating your heater differently from normal domestic household heating. These are explained in Eberspacher Technical Bulletin 281 which contains a lot of useful information.

Pressurised water systems are very uncommon and usually only used where a header tank cannot be fitted. Pressurised systems are out of our area of expertise and are not covered on these pages.

Some vehicles are fitted with Eberspacher heaters plumbed into the vehicles water system. Here the Eberspacher and the vehicles own water system are interconnected and the electrics may be linked into the engine management system. Fault finding is best suited to a garage mechanic so we do not give specific advice on these systems. You should also consult Eberspacher for advice if you are considering installing a water heater into the engine water system of a modern vehicle that does not have one fitted as the engine management system may detect the unexpected extra heat and decide it is a fault condition.

The Eberspacher Handiwash is an electric heater and is not covered here.

Two pipe and one pipe Header tanks

Eberspacher introAir HeatersWater heatersWater OEMSite guide
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Page 1 covers water heater introduction

Page 2 covers current models

Page 3 covers OEM models

Page 4 older models - page not available, it will be added at a later date.