Webasto / Espar: High Altitudes Usage


Webasto / Espar: High Altitudes Usage



The Webasto / Espar air heaters should be adjusted for high altitudes if the majority of it’s time is spent above 5000-6000 feet. As the altitude increase, the concentration of oxygen reduce and the mix of fuel/oxygen become too rich in fuel. This could lead to debris accumulation (a.k.a. coking or carbon) and loss of performance / malfunction. We know, because we had that issue with our Webasto and after a while it just wouldn’t start at all.

It is interesting to note that the Gasoline models are more prone to carbon accumulation than the Diesel models! This is counter intuitive because gasoline is more refined than diesel, but TechWebasto said it’s because “gasoline is less energy-dense than diesel“. We believe it’s true, because we have the Gasoline model and we had carbon issues quite fast…


For the Espar, the solution is to add a high altitude kit. Here is the installation manual.

“The kit automatically adjusts the fuel pump rate in relation to increasing altitude. As the altitude increases the fuel pump rate decreases. The High Altitude Kit adjusts fuel pump rate at all altitudes beginning at sea level.”

Espar High Altitude Module
Espar High Altitudes kit. Buy on Amazon



For the Webasto, there is no physical part to add; the unit must be programmed for high altitudes.

You can have it adjusted by a Webasto dealer, or it can be done using the rheostat:

Webasto Rotary Rheostat
Webasto Rotary Rheostat. Buy on Amazon.

If you’re having the SmartTemp or the MultiControl, you will have to buy (or borrow) a rheostat to make the adjustment.

Webasto SmartTemp
Webasto SmartTemp
Webasto MultiControl
Webasto MultiControl


Here is the high-altitude adjustment procedure:

(the procedure was confirmed by TechWebasto and it worked for us)


Changing the Webasto heater for high elevations (5,000ft and MORE) using the rheostat

On the main wiring harness, there is a wire that is used to make the CO2 calibration. Depending on your heater/controller model, the CO2 calibration wire is either brown (look for a 2-wires pigtail; there should be one brown wire and one green wire) or is either grey/red (look for a pigtail with only 1 wire; it’s close to the “Diagnose/Thermocall/Telestart” pigtail).

CO2 calibration wire. It should be located at the extremity of the harness (far from the heater unit itself).
The rheostat is connected to the pigtail labeled “USER POTENTIOMETER”. It should be located near the heater unit itself.
  1. Connect the CO2 calibration wire to ground (we connected it to our house battery negative, because our heater is connected to our house battery).
  2. Turn the heater control knob to 12:00 (or even 1:00 if you are at very high altitude 10,000ft plus)
  3. After a few moments (the heater will fire up and run for a few minutes), the LED on the heater control knob will begin to flash.
  4. Turn the heater control knob to 9:00 (or even 8:00 if you are at very high altitude 10,000ft plus)
  5. Keep the heater running with the control knob set to 9:00 for 3 minutes.
  6. While the heater is running, remove the CO2 calibration wire from ground.

Now the combustion fan is set to run faster, thereby creating a better combustion mixture for high altitude and less oxygen.


At that point, a Webasto dealer will actually check the adjustment by analyzing the exhaust gas when the heater is running; they have a machine that tells if the oxygen/fuel ratio is correct for the current altitude. We don’t have such a thing, but TechWebasto strongly recommended us to borrow an “Automotive Exhaust Gas Analyzer” from an auto service shop. We’re constantly changing elevation so there is no way to have the perfect setting, but at least the “Automotive Exhaust Gas Analyzer” gives a baseline for the adjustment (so it’s not done totally blind).


The tech said you can change it back when at sea level, but also said it was unnecessary, as the reduced fuel will not cause damage at sea level, just a lower heat output by 100-200 BTU/ hour at the maximum setting. He said that running it lean at sea level will also help to keep the combustion chamber clean. The Webasto Air Top 2000 ST/STC has a max BTU/h of 7000 so you are only losing at most 3%, and you are also reducing your fuel use, albeit marginally. Also, the system has Stepless temperature control, so you can feel free to turn it up 3% to regain your “lost” output all the way up to 97% output.


Changing the Webasto heater back for normal elevations (5,000ft and LESS) using the Stock Dial Thermostat
  1. Connect the CO2 calibration wire to ground (we connected it to our house battery negative, because our heater is connected to our house battery).
  2. Turn the heater control knob to 9:00
  3. After a few moments, the LED on the heater control knob will begin to flash.
  4. Turn the heater control knob to 12:00
  5. Keep the heater running with the control knob set to 12:00 for 3 minutes.
  6. While the heater is running, remove the CO2 calibration wire from ground.

Now the fuel pump should be set to deliver the stock amount of fuel, thereby creating a better combustion mixture for low altitudes and more oxygen.






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Hello! We’re Isabelle and Antoine 🙂 In 2017 we sold our house (and everything in it), quit our engineering careers and moved into our self built campervan. We’ve been on the road since then and every day is an opportunity for a new adventure; we’re chasing our dreams and hopefully it inspires others to do the same!




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You might be interested in these articles:

Webasto Air Top 2000 – How To Install a New Burner Following Carbon Buildup


Webasto Air Top 2000 Heater Installation


Webasto Air Heater Noise Reduction



39 thoughts on “Webasto / Espar: High Altitudes Usage”

  1. Hey, has anyone used the MultiControl Timer to adjust for high altitude on the STC 2000? Curious to hear about your experience and if the heater still works well after adjusting

    • You can’t use the MultiControl HD to make the adjustment, UNLESS you have the Air Top 2000 STC “RV” model specifically. Otherwise, the adjustment must be performed using the rotary control (once the adjustment is performed, you can use the MultiControl HD). That’s what we did and it’s working fine!

      • Thanks for the info, Antoine! I adjusted my altitude setting when I was at 5,500ft but after running my Gasoline AirTop STC 2000 for about a week at 9,000ft, the chamber flooded which caused an F02 error. I’m thinking that my heater was running “thin” for 5,500ft but that it was just pulling too much gas to run properly at 9,000ft. When adjusting the altitude setting, my understanding is that you’re adjusting it to run “thin” at the altitude you’re currently at…is that your understanding too? Have you successfully run your heater at altitudes around 9,000ft?

        • Yep, if it’s adjusted for 5,500ft it’ll run too rich at 9,000ft… We spent a week at Mammoth (8,000ft?) and didn’t have any issues, but we didn’t use the heater much.

        • Hey Brayden,

          I think I’ve just encountered the same problem. I adjusted my STC per the instructions in this article to run as thin as possible, but I made that adjustment at sea level. I’ve now been running the heater at 9,000’ for a week and just encountered an H03 code in the multicontrol. Webasto tech support suggested that I had carbon buildup or that it’s still running too rich.

          Were you successful after you made the adjustment again at 9k’?

      • Antoine, can you clarify what you mean “once the adjustment is performed, you can use the MultiControl HD”? Do you mean “use the MultiControl HD” for normal operations or use to perform subsequent elevation adjustments? We move around elevations a lot and it seems like a pain to remove the passenger seat and hook up a rheostat every single time. Given the rheostat seems to be designed for permanent installation, cost not being an issue, would it make sense to just install the rheostat permanently as well as a switch to connect the ground wire in a convenient place? Or does the rheostat need to be unplugged as well to use the MultiControl HD? I haven’t poked around on the wiring harness to see where the connector is (and a good ground source as well). Seems the easier this procedure is to do the more likely I am to do it at the proper times and keep the heater working well longer (realizing it’s just a guess without a gas analyzer but hopefully better than nothing for going from sea level to 9k feet). Thoughts?

        • I honestly don’t know if the rheostat has to be unplugged, but my guess is yes… What we did is we adjusted it for high altitude (for around 6,000 ft I believe) and leave it permanently like that; it doesn’t hurt to have it adjusted for high altitude and use it at lower altitude.


  2. Hey, thanks for all the valuable information on your site!

    I live at sea level and will be traveling to high altitudes over 5000ft. Do you think the airtop STC can handle a week of this with out adjustment? I unfortunately don’t own the rheostat. I appreciate your input.

  3. Hey Guys!

    How did you connect the CO2 calibration wire to ground? It looks like it has that odd white connector on the end. I assumed you snip this off? Thanks!

  4. I have the 2000STC and Webasto Rotary Rheostat. I have the Webasto harness that is specific to the Rotary Rheostat and as far as I know it will not accommodate any of the other controllers (SmartTemp or MultiControl). I absolutely need to make this altitude adjustment.
    Does anyone know: 1) Which end of the this harness (heater-unit end or Rheostat-end) the CO2 calibration wire is? and, 2) What color the C02 calibration wire is?
    Also, can the Webasto dealers in the US now do this procedure? I would rather get it done by them so they can use the exhaust analyzer to confirm the results.
    Thank you,

      • Thanks Antoine. Well, I think that I have answered my own question. On the ButlerTechnik website you can download the Webasto technical manuals. What was confusing me is that, for some reason, I have ended up with a harness that matches the wiring diagram shown on page 702 of the manual for the 2000ST heater, even though mine is a 2000STC. In any case, the heater functions. So, I am pretty sure that the brown wire on the pigtail at the heater end is the one I need to ground to do the altitude adjustment. I would still very much like to analyze the exhaust gasses to make sure the adjustment procedure has done something. Has anyone thought of cajoling someone at a SMOG station into using their exhaust gas analyzer machine? Assuming I can do this, does anyone know what I would be looking for in the printout from that machine? Andrew

  5. Hey Antoine..last couple questions lol..did u switch back to the multi controller after the altitude adjustment with the Rheostat? Also have you cut the power to the Webasto since you did the altitude adjustment? I have read a couple things on the internet that says the adjustment is permanently stored even with power cutoff but wanted to make sure.

    Thanks again.

    • Hey,
      yes we switched back to the MultiControl HD after. I emailed TechWebasto and they confirmed me that the altitude adjustment is permanent (even if you cut the power after).


  6. Hey Antoine..quick question..did you leave the Smart Temp or Multi Control (not sure which controller you have) plugged in while you adjusted the altitude with the Rheostat or did you have to disconnect the Smart or Multi controller first?

  7. This heater installation has been quite the project.
    Did you guys have any trouble connecting your rheostat to the wiring harness that came with the Smart Temp controller?

    I just ordered a rheostat, but it appears to want a 4 pin female control connector.
    There isn’t anything like this on the wiring harness that came with my unit (that connects to the smart temp controller).

    • Hey,
      We connected the rheostat to a pigtail labeled “User Potentiometer”; ours was located near the heater unit itself (under the seat):
      Webasto Rheostat Pigtail

      Hope that works!

  8. I just gave it a try and wasn’t able to get it to work. A would get an error code (“Fault F00”) after a few minutes when I started the SmartTemp with the brown wire grounded.

    Apparently I’ll either need to buy a rheostat, or find a dealer who can adjust the unit.

      • FWIW… I tried with the smartemp controller and was not successful – ended up with repeated f14 and f15 error codes. Had to reset the heater to get it working again. Curious if anyone has been successful with the smartemp without going to a dealer?

  9. Reading through their literature, it sounds as though the Multi-control should have the ability to put the unit in to the high altitude mode. There is a manual switch which is available to do this for the thermostat control options but the install manual states that the switch isn’t for use with the W bus connections (multi-control). I emailed Webasto UK in hopes that it is as easy as a setting on the multi-control.

    Those directions from the Samba post appear to be using the CO2 calibration procedure to effect the same change. It appears that those directions are for an Airtop 2000 ST, although they should work with the STC only replacing the brown wire with a green/red wire.

    We live in CO at 7,500 feet and many of our adventures are higher than that, hence my need to figure this out. Thanks for all the information that you guys have published, your site is one of my go-to resources. If you ever find yourselves in CO I’d love to buy you some beers and maybe show you some secret pow stashes ;).

    If I figure anything out I will let you guys know.

      • It appears that there may be more readily available tech support in NA soon. I came across a AT2000STC_USA operations manual on the tech webasto site. It’s release date was August 7th, 2017, so hopefully the tech support people at Webasto USA will soon be of some use for the STC model heaters.

    • Nope, we’re still in the flat lands (and summertime) so this will have to wait… Our guess is that we will have to do it at a Webasto shop; we’ll keep you updated!

      Have a good one,


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