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Derek's general tips and notes.
Start failures after first installing.
Ok, you've followed all installation instructions; checked your battery voltage; and switch it on. 60 seconds later, motor speed increases and fuel pump starts to tick - only to shut down again after a further 90 seconds. If left alone it tries again - often with same result. Panic!
No problem. What you have probably overlooked is that the fuel pump needs to prime itself and the fuel pipes before it can supply the heater. If the flame sensor fails to detect a flame within 90 seconds of pump starting, the ECU automatically aborts the start, then tries again. Now, assuming you are using the correct piping (1.5mm i.d.)  each start attempt theoretically supplies sufficient fuel to fill around 2.26mtrs of pipe. But don't forget that the inlet pipe from fuel supply to pump, and the pump itself needs to prime first. How much fuel is required here depends on the distance between supply and pump, but the correct 2mm i.d of this pipe will fill at the reduced rate of 1.27mtr per start. So an overlength pipe can demand several start attempts before the fuel even reaches the pump.
If you are using clear plastic piping on the outlet side, the fuel flow can be observed by tiny evenly spaced bubbles, but even when it shows full more fuel is needed to reach the glowpin chamber and main burner. And if this point is reached a few seconds short of the 90 second mark the heater can fire up, but cut off again before the flame sensor can register. Remember the heater will automatically make two start attempts, but you will then need to switch off and re-start it again. Also, if you are using pipes with larger inner diameter size, more start attempts will be required. Once primed, your heater will fire up on first attempt each time unless you have a fuel leak somewhere, or disconnect a pipe for any reason.


Pre-Winter check  (September/October)
Winter has arrived, and you switch your heater on for the first time. It worked perfectly last winter, but now horror! You have trouble - at the time you least wanted it. Check it now to minimise the risk of trying to fix it in freezing conditions. Give it a run at full heat and speed for an hour - if it will do so. Summer temperatures and humidity can so easily come back to bite you and your system can prove a desirable nesting place for insects or worse. I remember some years ago when my blown air ducting delivered a mouse nest complete with occupants into my living area. Combustion air inlet and exhaust system also make ideal homes.
Even if your unit performs ok there are still points worthy of consideration. Check your fuel tank for a build-up of debris and water at the bottom. If the heater picks up any of this it can cause starting problems. Check battery condition and all connections between it and heater. The heater will not run unless it is receiving at least 10.6 volts. During the first 3 minutes from switch-on it will draw between 11 and 23 amps depending on the model, and voltage will usually be at its lowest at this stage.
A cloud of exhaust smoke on the first start-up is often due simply to stray dust, carbon particles etc and water accumulation, but if it persists on following cold starts, or was doing so when you last used it this indicates that it is clogging with carbon and a clean-out service is due. Otherwise it will reach the point where heater will not start. Many experienced Eberspacher owners advocate running a litre of pure paraffin, or kerosene (aka domestic 28 second central heating oil or commercial paraffin) through on high heat setting to clean out most of the carbon. Unfortunately while this is basically correct, it is unlikely to clean out the glowpin screen which is a notorious choke point. I fully support Eberspacher's recommendation that a new screen is fitted at least every 2000 hours of running; and while you are at it you may just as well do a complete service. Just follow our service guide, and you should not find it difficult to do. Having said this, two years ago my D2 clogged up during a -11c spell, and as an emergency I tried kerosene. This is the only fuel I have used since, and so far have clocked up just over 4000 hours of running (excluding standby time) without a service or any sign of trouble. Looks as though it will do at least another 4000 at least. Even so, I always carry a spare glowpin screen and burner gasket. As such my D2 will be fully serviced, back up and running within 2 hours, without a long wait for spares to arrive.
Generally most failures occur somewhere in the startup sequence. In these cases check the sequence of your model in our faults section, and identify exactly where yours fails. Match it against our faults list to indicate the cause. Also, if you are using red diesel check its condition, as it degrades badly over a period of time. Symptoms are excessive exhaust smoke, fuel has turned darker, layers of black sludge in bottom of tank. These are all symptoms of Diesel Bug; a bacteria becoming more common, particularly in red diesel where the fuel is not regularly replenished.
Of course your problem could be more serious than mentioned above, but surely it is better to sort it out now rather than wait until brass balls begin to be mentioned, and you join the hoard of other users desperately scrabbling to obtain vital heat.


Blown air ducting systems
Having dealt with all major heater problems it is now worth considering potential ones in your blown air ducting.
At face value it is relatively simple to convey your heated air to the point where it is most needed by installing lengths of heater ducting pipe between heater and outlet. However, there are issues which can impair the heater's performance to a great extent. In the first place, all ducting is susceptible to airflow restriction due to drag factors; and the longer the pipe the greater the restriction. Try blowing through a 20cm length of garden hose, then do the same through a 10 metre length and you will see what I mean. This restriction is further increased by "T", "Y", or elbow joints, plus curves, bends and twists in the ducting pipe itself. This situation is easily overlooked as nothing obvious shows. However, it can reach the point where back pressure and heat buildup at the heater end forces heater into overheat mode, or sends it into standby at a lower temperature. And you can't understand why, so tend to blame the heater itself. After all everything looks ok - been there myself so I know. Have a good look at the Eberspacher chart on this subject and prepare yourself for some surprises.
airtronic_d2-4-5_marine_heater_22278.pdf
Each bend, connector, metre length, outlet vent etc quoted on the chart is for a single unit, so multiply by the number you have in your system and add them for a total. Now check against the rating given for your heater model, which is the maximum figure it can comfortably handle. If your total is well above the rating number, it can often be reduced by re-routing the ducting to eliminate bends etc. Also Y piece connectors rate lower than T. 75mm ducting is lower-rated than 60mm but usually needs a larger heater outlet hood. If you have more than one outlet vent the airflow can be split between two duct pipes. In this case an adjustable Y piece connector from ebay will enable you to control the flow to each pipe. Alternatively, a T piece mounted to supply second pipe at a 90 degree angle will deliver a reduced supply to this one.

With this problem solved there is still a further point to consider - heat loss between heater and outlet ducts. Not an issue for short ducting, but can be considerable over a distance. Insulated ducting is available, but is pretty expensive. Strange how any item which can be associated with the word "boat" seems to attract a premium price. However, wrapping standard loft insulating roll around my ducting has worked well for me, and it is completely capable of coping with the relatively low temperatures of the heated air.

Have a warm winter.