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Hydronic D10W & Hydronic M Service and Repair

Thanks to Mr & Mrs Clarke for donating this beyond economic repair D10W to our collection.

Click on images for better quality.

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Disassembling Hydronic D10W & Hydronic M


Eberspacher Hydronic M is the same heater with a newer version ECU so disassembly is the same.


Eberspacher Hydronic D10W


Cutaway view of Hydronic D10W.

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Undo the 3 crosshead screws holding the ECU.

On this heater one screw is missing.


Press in the retaining latch and unplug the connector.

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Remove the Glowpin top nut with a 7 mm spanner or socket.


Remove the glowpin seal with a small screwdriver.

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Ceramic glowpins should last the life of the heater. Clean off any carbon deposits, this one is fairly clean. Knobbly deposits usually indicate water in the fuel.


Remove the cable cover.


Use a 4 mm hex key to remove the four bolts holding the blower end cover and the blower. White mark on impeller is for blower speed measurements.


The blower motor is wired into the ECU connector. The impeller on this heater has been glued onto the shaft with the motor screws under it so motor cannot be repaired.

The impeller clearance is 0.3 mm as shown on faults page.

Pull the cable slack outside the heater.


All the cables terminate in this 18 pin ECU connector. Fortunately on this heater normal servicing can be done without disconnecting the cables.


Use a 4 mm hex key to remove the four fixing bolts.

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Terminals cannot be removed without an extractor. More details on wiring page. This connector is described in the Mouser catalogue as a

Junior Power Timer housing AMP 929504-6

The connector will pass through the cutout.

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The 4 screws holding the burner have been exposed to the exhaust gasses and these are rusty or corroded.


Three sections all wired together means an extra pair of hands is useful when they need to be moved.

There should now be enough cable to allow the heat exchanger section to separate.


With no compression fitting the grommet does not have to be pushed out of position but if compression fittings are on the fuel pipe as here the grommet hole is large enough for them to pass through the case as shown.


Another view of those screws. Surprisingly these came out reasonably easily. The flame sensor protrudes into the path of the exhaust gasses near the exhaust port outlet.


In the burner glowpin hole is a fixed non replaceable screen which is difficult to see. This one had some minor deposits visible but not enough to cause problems.

The D1L servicing pages show a similar screen illuminated.


The fuel pipe passes through a second grommet identical to the first one. The other side of grommet is shown in earlier photo 'Use a 4 mm hex key to remove the four fixing bolts'. Ease the burner out.


The second ventilation hole is upper centre.


There are two ventilation holes in the side of the glowpin tube. One is visible here. Ensure both are clear of deposits. Some burners may require chemical or industrial ultrasound cleaning as a mechanical clean cannot reach hidden parts. Any chemical cleaner can be dangerous, always follow manufacturers instructions. For health and safety reasons we make no recommendation but many users clean with caustic soda.


The central dark area is just a burn stain. Around that is a raised metal plate covering 4 spiral guides. On top of the plate is a fibre sealing washer. Blown air enters through the square shaped hole upper left. The air rotates anti clockwise and passes through the spiral paths to the centre where it enters the burner.

Inside the burner is a wire mesh, probably similar to this one shown in a cutaway model MII. The mesh can become clogged by deposits and can deteriorate with prolonged use, see the D4 example in autopsy pages.


Remove the two fixing screws.


The inside of the heat exchanger is fully accessible and the deposits can be removed by mechanical or chemical cleaning.

At this point the two parts of this heat exchanger would not separate. It is not necessary to get inside these parts for normal servicing so this should only a problem if the sealing ring has failed. The overheat and temperature sensors probably have to be unscrewed first, they cannot be removed without disconnecting the wires from the 18 pin connector which requires a suitable pin extractor which we do not have. Or you could cut the wires and rejoin them later. There are two indentations in the casing presumably to help separation using a flat bladed screwdriver. A large flat screwdriver inserted into the water inlet could be used as a last resort.


Thanks to an ebay seller for these photos of a D10W heat exchanger.


D10W exploded parts drawing.


After mechanical or chemical cleaning the burner and heat exchanger the heater can be re-assembled. Assembly should be the reverse of taking apart. O-rings should be lubricated with silicone or other suitable lubricant. Two of the gaskets are shown in the exploded parts drawing as needing silicone sealant. For refilling or topping up use a 10 to 50% antifreeze mixture, it also prevents corrosion. The fuel pump is separate from the heater and contains a filter which should be checked. Details are on the D2 and D1LCC service pages.

This servicing kit for the D10W on Ebay was £24 in December 2014.

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D10W bottom view.

Flame sensor is just visible in exhaust port.

D10W rear view.

Water pump is fixed by a jubilee type clip.

D10W side view.

Water pump inlet bottom.

This D10W Label is rather faded. It says

Type - Hydronic 10

Ausfeuhrung - D10W

D10W Top and ECU.

Hot water output centre with temperature sensor above it. Overheat sensor left.

The retaining latch can be seen on the free connector.

The ECU is encapsulated in black potting compound.

The earlier cutaway picture shows a little more detail.

Remove the glowpin with a 1/2" 13 mm socket.

My 3/8" socket was not deep enough.

Tip: Refit the nut after removal to avoid losing it.

Eberspacher Servicing D2 D4 D5 D1LCC D1L D3L Hydronic
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