Eberspächer Airtronic D2 – Heater
Photo: Eberspaecher, CC BY-SA 3.0, via Wikimedia Commons (cropped)

Eberspächer · Heater

Eberspächer Airtronic D2

The Airtronic D2 is Eberspächer’s 2.2 kW diesel air heater, sold as the Espar Airtronic D2 in North America, and a common retrofit cabin heater on smaller sailing and motor boats, usually as the 12 V diesel version with the marine exhaust kit. It draws diesel from the boat’s tank through its own metering pump, burns it in a sealed combustion chamber and blows cabin air over the heat exchanger. The original D2 (2001–2018, 12 or 24 V) regulates in four stages; its 2018 successor, the Airtronic S2 D2L, brought a brushless blower, stepless control and a CAN connection for EasyStart Pro and Web, with a new glow plug, sensor, blower and control box but the same glow pin screen, burner gasket and base seal. Since 2021 the Airtronic S3 D2L is the current model; the 4 kW sibling, the Airtronic D4 (M2 D4L), has its own burner parts.

Manuals & documents

The links go to Eberspächer’s own documents — some as archived copies of pages the maker has since taken down. We host no manuals or drawings.

Wear parts & part numbers

PartOEM numberAlso fitsNote
Service kit29.2199.01.54071,2,3,4—Original Airtronic D2, 12 V and 24 V: blower gasket 25.2069.01.0003, burner gasket 25.2069.06.0001, glow pin screen with fitting tool 25.2069.10.0102 and metering-pump strainer 20.1312.00.0006. A distributor kit number, not in Eberspächer’s parts list. The S2 D2L takes a different blower gasket (25.2721.01.0003).
Glow pin25.2069.01.1300 · 25.2070.01.11003,5,6,7,8,4—Original D2: 12 V / 24 V, each with socket wrench (the 12 V pin also fits D3, D4, D4 Plus and B4, the 24 V pin D4 and D4 Plus). Not for the S2 D2L. Resistance at 20 °C: 0.42–0.70 Ω (12 V), 1.2–2.0 Ω (24 V).
Glow pin25.2720.99.0106 · 25.2729.99.01064,9,10—Airtronic S2 D2L: 12 V / 24 V, each with socket spanner (also M2 D4L; the 12 V also D4R and B4L). Not for the original D2. Butler Technik: the 24 V pin itself is marked 25.2729.01.0600.
Glow pin screen25.2069.10.01023,4,11,12—Lines the glow pin socket; the same for D2 and S2 D2L. Replace it when it is carboned; it comes with its own fitting tool.
Combustion chamber25.2069.10.0100 · 25.2721.99.10003,5,13,4,14—With gasket: original D2, 12 and 24 V / S2 D2L, with screws. The 4 kW heaters take their own: D4, D4 Plus and D3 25.2113.10.0100, M2 D4L/D4R 25.2720.99.1000. Butler Technik ships the D2 chamber with a glow pin screen.
Combustion chamber gasket25.2069.06.00013,5,4,15—The same for D2 and S2 D2L. D4, D4 Plus and M2 take 25.2113.06.0001.
Blower gasket25.2069.01.0003 · 25.2721.01.00033,5,4,16,17—Original D2 / S2 D2L. D4 and D4 Plus take 25.2113.01.0003, M2 25.2720.01.0003.
Base gasket25.2069.01.00023,5,4,18—Flange seal between the heater and its mounting surface; the same part for D2, D4, S2 D2L and M2.
Flame / overheat sensor25.2069.01.0200 · 25.2720.99.40003,5,19,4,20,8—12 and 24 V: original D2 with fitting tool (also D3, D4, D4 Plus, B4) / S2 D2L with connector (also M2 D4L/D4R, B4L). Not interchangeable between the generations. D2 overheat switching point 140–170 °C; codes 064/065 and 071/072 point here.
Fan drive assembly25.2069.99.2000 · 25.2070.99.20003,5,21,22—Blower for the original D2, 12 V / 24 V: motor with the combustion-air and hot-air impellers. Butler Technik: the factory-fitted 12 V motor may be labelled 25.2069.20.0200.
Fan drive assembly25.2721.99.1500 · 25.2726.99.15004,23,24—Brushless blower for the S2 D2L, 12 V / 24 V, with screws. Does not fit the original D2.
Control unit22.5101.00.3001 · 22.5102.00.30013,25,26—Original D2, 12 V / 24 V (Eberspächer list 11.2009). Butler Technik gives 22.5101.00.1001 / 22.5102.00.1001 as the older numbers. Cargo-heating (ADR) versions and North American Espar heaters have their own boxes.
Control unit25.2721.99.50004,27—S2 D2L, 12 V. The 24 V box appears in only one source and is left out.
Heat exchanger25.2069.06.01003,5,28,29—Original D2, with gasket; complete with combustion chamber 25.2069.99.0600. D4, D4 Plus and D3: 25.2113.06.0100. Eberspächer: replace ten years after first commissioning. The S2 D2L heat exchanger appears in only one source and is left out.
Fuel dosing pump22.4519.01.0000 · 22.4518.01.00003,5,30,31,8—Original D2, 12 V / 24 V (also D4 and D4 Plus; the 12 V also D3). Coil resistance at 20 °C: 9.5 ± 0.5 Ω / 36 ± 1.8 Ω. Fuel quantity test: 3.5–4.3 ml in 90 s.
Fuel dosing pump22.4552.03.0000 · 22.4553.01.00004,32,33—Airtronic 2 (S2 D2L, M2) and Airtronic 3, 12 V / 24 V, electronically controlled. Butler Technik: the 12 V pump does not fit a first-generation Airtronic (before 2019) without an adapter lead.
Inlet strainer20.1312.00.00063,5,4,32,34—Pot-type strainer in the metering-pump inlet; the same for D2, D4, Airtronic 2 and Airtronic 3, and part of the D2 service kit.
Wiring harness25.2069.80.0200 · 25.2720.80.11003,35,4,32,36—Connects battery, control element and metering pump: original D2 and D4 / S2 D2L, M2 and Airtronic 3 (CAN).
Control / rheostat22.1000.32.070037,5—Airtronic mini controller (rotary knob, heat/vent) for the original D2 and D4; the S2 D2L can use it on its S+ interface.
Control / rheostat22.1000.35.22004,32,38,39,40—EasyStart Pro, 7-day timer with diagnosis, for the CAN-based S2 D2L and S3 D2L only; not for the original D2. Butler Technik also lists 22.1000.35.2300. To fit an S2 or S3 in place of a D2 and keep the old wiring and controller, dealers sell plug-in adapter harnesses.
Control / rheostat22.1000.35.350041,42—EasyStart Web, app and remote control with built-in SIM; the current version since 09/2021, earlier 22.1000.34.5100 (05/2019) and 22.1000.34.7800 (06/2019).
Control / rheostat22.1000.34.130043—EasyStart Select room-temperature controller. One source (Butler Technik): works on an original D2 only with the newer control box marked “H-Kit” on the type plate, and on the S2 D2L in 12 V only.
Exhaust silencer25.1864.81.01003,4,32,45Webasto 9014067A4424 mm vehicle silencer for D2, D4, S2 D2L and Airtronic 3. Butler Technik: not for marine use; on a boat fit a gas-tight stainless marine silencer such as Webasto’s 9014067A (24 mm, formerly 1322001A), which the dealer lists for the Airtronic D2.
Exhaust pipe (heater)360.61.29946—Marine version: flexible double-wall stainless pipe, 24 mm i.d., by the metre, usable without restriction on the D2 (and D3/D4/D4 Plus, D5). One source, Eberspächer’s marine catalogue from before 2010; some items may since have changed.
Exhaust elbow with condensate drain25.1226.89.450046—24 mm / 24 mm, with an M10×1 condensate drain, for D2, D3/D4/D4 Plus and D5; the 24-to-30 mm version is 22.1050.89.3900. One source (Eberspächer’s marine catalogue from before 2010).
Exhaust hull fitting22.1050.89.430046—Polished stainless, 30 mm o.d., 90 mm flange. Marked “with restrictions” for the D2 because its exhaust is 24 mm: it needs the 24-to-30 mm transition piece 25.1520.80.0101. One source, Eberspächer’s marine catalogue from before 2010; some items may since have changed.
Hot-air duct10.2114.31.0000 · 10.2114.34.00003,4,32,47,29,48—By the metre, 60 mm / 75 mm. The D2 universal kit has a 60 mm outlet; Eberspächer recommends the 75 mm ‘Plus’ kit for boats, and the S2 D2L comes with a 75 mm hood. With 60 mm hose the D2 allows only a short duct run, with 75 mm a longer one or a second outlet. Always leave one outlet open, or the heater shuts down overheated (012/013).
Installation kit29.2113.30.002549—Complete marine heater kit Airtronic S3 D2L 12 V with two outlets and EasyStart Pro (Eberspächer UK kit number): the current replacement for a D2 or S2 on a boat. One source (Butler Technik).

Numbers checked against the sources below on 13 October 2026. Always confirm against your serial number and exact type before ordering.

Service intervals

TaskInterval
Monthly runOnce a month for about 10 minutes, outside the heating season too, so the metering pump, fuel line and burner do not gum up50,29,51
Season checkTrial run before every heating season; if it smokes heavily, smells of fuel or sounds unusual, switch off, pull the fuse and have it checked50,29
Storage / winterisingAfter a long lay-up: check that all screws are tight, look for fuel leaks and clear the hot-air, combustion-air and exhaust openings47,50
Strainer cleanClean or replace the metering-pump strainer once a year, more often with dirty fuel (Espar North America)12
Heat exchanger cleanReplace with a genuine part ten years after first commissioning (year on the type plate) and stick the “original spare part” label next to it29,47

Schedule from Eberspächer’s Airtronic / Hydronic operating instructions (2025), the Airtronic S2 / M2 technical description (2024), the 2009 Airtronic technical description and Espar’s Airtronic D2 / D4 diagnostic and repair manual (2013).

Specifications

Heat outputOriginal D2: 850 / 1200 / 1800 / 2200 W in four stages (approx. 2900–7500 BTU/h); S2 D2L and S3 D2L: 0.85–2.2 kW stepless47,29,52
Fuel consumption0.10–0.28 l/h diesel (original D2 by stage 0.10 / 0.15 / 0.23 / 0.28 l/h)47,29
Power consumptionOriginal D2: 8–34 W running, 5 W during fan after-run, up to 100 W while the glow pin heats at start. S2 D2L: 6–31 W, max. 100 W at start, 100 µA on standby. S3 D2L: 6–28 W47,29,52
Voltage12 V or 24 V; under-voltage cut-off approx. 10.5 V / 21 V (S2 D2L: 21.4 V), over-voltage cut-off approx. 16 V / 32 V, each after 20 s47,29
Air flowUp to 105 kg/h without back-pressure: original D2 with 60 mm outlet hood 105 / 90 / 60 / 40 kg/h by stage, 13 kg/h in after-run; S2 D2L with 75 mm hood 105–42 kg/h47,29
FuelDiesel EN 590. Original D2: max. 10 % FAME, no biodiesel. S2 D2L: max. 30 % FAME, also HVO/GtL (EN 15940), no pure biodiesel. Heating oil EL only above 0 °C and from a separate tank; never add used oil47,29
PortsExhaust 24 mm i.d., combustion-air intake 25 mm i.d., each 0.2–2 m long and laid with a slight fall (drill a 5 mm drain hole at the lowest point if needed); fuel line 2 mm i.d., max. 5 m from tank to metering pump and 6 m from pump to heater; hot air 60 mm (original D2) or 75 mm (S2 D2L, D2 ‘Plus’ kit)47,29,48
Max. installation angleBest with the exhaust, fuel and combustion-air connections pointing straight down; runs at a permanent 15° heel and, once started, up to 30°48
Breaker / fuseOriginal D2 (and D4): 5 A + 20 A at 12 V, 5 A + 10 A at 24 V48
Power cable size4 mm² up to 5 m (plus and minus together), 6 mm² from 5 to 8 m48
Tightening torquesGlow pin 6 +0.5 Nm8,12
Test valuesOriginal D2: glow pin 0.42–0.70 Ω (12 V) / 1.2–2.0 Ω (24 V) and metering-pump coil 9.5 ± 0.5 Ω / 36 ± 1.8 Ω, each at 20 °C; fuel quantity test 3.5–4.3 ml in 90 s; overheat switching point 140–170 °C8,12
Fault codesOriginal D2, three-digit codes read with the timer, EasyStart or a diagnosis unit: 000 no fault · 010 over-voltage · 011 under-voltage · 012/013 overheating (overheat / flame sensor) · 014 temperature difference between the sensors too large · 015/017 overheat lock-out (control box locked) · 019 ignition energy too low · 020/021 glow pin open / short · 031–033 blower open / short / wrong speed · 047/048 metering pump short / open · 050 too many failed starts (lock-out) · 051 flame detected at switch-on · 052 no start (safety time exceeded) · 053–056 flame-out in power / high / medium / low stage · 060/061 external temperature sensor · 062/063 control element open / short · 064/065 flame sensor · 071/072 overheat sensor · 090–099 control box faults (091 interference voltage, 099 voltage dips). S2 D2L, LED flash codes: 1 lock-out after overheating · 2 over-voltage · 3 under-voltage · 4 glow plug · 5 burner motor · 6 invalid configuration · 7 no start (safety time exceeded) · 8 overheating · 9 metering pump · 10 external temperature sensor / set-point · 11 combination sensor · 12 flame-out · 13 too many start attempts · 14 control box · 15 other fault, needs EasyScan, which shows P-codes (e.g. P00012A = 052 failed start, P00012B = 050 lock-out)8,53
Lock-out resetAfter a failed start or flame-out the heater tries once more, then shuts down with about 4 minutes of fan after-run; switch off and on to clear it, no more than twice. Original D2: repeated failures set 050 and lock the control box until the fault memory is cleared with a timer, EasyStart or diagnosis unit. S2 D2L: locks after 10 failed starts or 10 overheat shutdowns; clear an overheat lock by switching on, pulling the heater fuse within 20 s and refitting it after about 5 s47,8,53
Weightapprox. 2.7 kg (D2 and S2 D2L); S3 D2L 2.5 kg47,29,52
Dimensions310 × 115 × 122 mm (L × W × H; the same main dimensions for the S3 D2L)54,52
VersionsAirtronic D2, 12 V and 24 V (2001–2018; also a D2 Camper version; Espar Airtronic D2 in North America) → Airtronic S2 D2L (from August 2018) → Airtronic S3 D2L (from 2021). The 4 kW sibling is the Airtronic D4, later M2 D4L. The order numbers on the type plate are in the first tip below55,56,57,47,29,58

Good to know

  • Read the type plate before you order: 25.2069.05.0000 (12 V) or 25.2070.05.0000 (24 V) is the original Airtronic D2, 25.2721.05.0000 / 25.2726.05.0000 the S2 D2L and 25.2953.05.0000 / 25.2954.05.0000 the S3 D2L. Glow pin, sensor, blower, control box and metering pump differ between D2 and S2; glow pin screen, burner gasket, base seal and casing are shared. Eberspächer numbers turn up as 25 2069 01 13 00, 25.2069.01.1300 or 252069011300: all three are the same part.47,8,29,58,4
  • Switch it off at the control element, never with the battery isolator: the fan runs on for about four minutes and the glow pin glows for about 40 seconds to burn the chamber clean, and cutting the power skips that. Espar also asks for at least 15 minutes per run: short cycles, a flickering switch-on signal or a heater far too big for the cabin soot up the burner, so find the cause before you replace the combustion chamber.47,12
  • No start (052, flash code 7): check the fuel level, the metering-pump strainer and the fuel line for air leaks, that intake and exhaust are clear, then glow pin and glow pin screen. Switch off and on again at most twice; after repeated failures the control box locks. Under-voltage (011, flash code 3) is usually a weak battery, a fuse, corroded terminals or a supply cable that is too thin or too long: the start draws up to 100 W.8,48
  • Whenever the glow pin is out, look at the glow pin screen (25.2069.10.0102): replace it if it is carboned (it comes with its own fitting tool), make sure the small vent hole next to it is open, and tighten the glow pin to 6 Nm.12,3,4
  • On a boat use a twin-wall stainless exhaust and a hull fitting on a vertical surface, never on deck (transom preferred; on a motorboat transom at least 300 mm above the waterline). Route it so water cannot run back into the heater, fit an elbow with condensate drain where needed, and never join it to the engine exhaust. The standard vehicle silencer is not meant for boats.48,45
  • Take the fuel from a dedicated standpipe in the top of the tank rather than teeing into the engine feed, cut so it ends at least 25 mm above the tank bottom, and mount the metering pump with its outlet side rising (15–35°). After filling up with winter diesel, run the heater for 15 minutes so the line and pump hold the new fuel.48,29,50,47

Fitted in

Boats whose builder lists it as standard or optional equipment:

  • Pogo 12.50 — Eberspächer Airtronic D2 (Option in the 2010–2012 lists: diesel air heater with two outlets)

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Sources

  1. butlertechnik.com/item/Eberspacher/D2-Airtronic-heater-service-kit-292199015407/5CD
  2. everythingcaravans.com.au/products/eberspacher-full-service-kit-for-d2-diesel-heater
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