Any Webasto experts here?

Mar 11, 2015
357
Hunter 33.5 Tacoma, WA
My Webasto gave out a couple of months ago and since it was summer I figured it could wait, but it would be real nice if I had hot water again [grin].
It is a Thermo Top Z/C, 12V, 5kw model, plumbed for cabin heat and hot water.
Here are the symptoms:
1) Turn thermostat until it "clicks"
2) The click coincides with another relay click I can hear on the surewire water board.
3) The surewire board has as green light, and the hour meter reads 2400 hours.
3) I measured terminal "x2" (main power), at the heater, and it has 12v.
4) Other than the click from the relay, silence.
5) I did try the "reset" procedure.

Question: If power is present on the X2, should the Webasto immediately start spinning, or are there other interlocks that would prevent this?

Thanks!
 
Mar 11, 2015
357
Hunter 33.5 Tacoma, WA
MZ, they are good folks. Located in Ballard. My friend has used them several times. Always found them helpful.
Thanks Mark and JS. I will certainly give them a call. I have also been studying the shop manual and schematic, and they don't seem as complex as I originally thought. I'll post what I find.
 
Mar 11, 2015
357
Hunter 33.5 Tacoma, WA
UPDATE: After spending the afternoon with my head deep in the lazerette, I may have found the smoking gun. At the same time, I learned a LOT about this unit, so I'm sharing this for the benefit of others who may be brave (or foolish) enough to try and fix this thing yourself.

There are 5 waterproof terminal plugs connected to the main circuit board on the Webasto unit.
X1 - Dosing pump
X2 - Main power
X3 - Glow Plug/ Flame sensor (Webasto internal)
X4 - Combustion Air fan (Webasto internal)
X5 - Circulation Pump

As part of troubleshooting, it is useful to check the resistance: On my unit, I got the following readings:
Dosing pump: 5.3 ohms, Glow Plug: .3 ohms, Air Fan: 5.7 ohms, Circ Pump: 4.0 ohms

So, no "open" circuits. I expected the glow plug to be open, but it wasn't. Next, for each component, jumper 12VDC to verify operation:

Air Fan: Spun perfectly
Circ Pump: Pumped normal
Glow Plug: Didn't test this since resistance was normal
Dosing Pump: "Thunked" with 12V applied, not the "clicking" I expected

Checking further, the dosing pump seemed odd to me because I always heard "clicking" before, but I still wasn't sure:

Disconnected main fuel line to Webasto unit, jumpered the dosing pump, nothing pumped (only thunks). There was an inline fuel filter, which I took apart and cleaned. It was clean enough (I could blow through it), so at THIS point I believe I have a faulty dosing pump. This makes sense, because the shop manual says the Webasto will go into "lock" mode if it fails to fire up 3x.

Still, I am puzzled that the Air Fan does not spin, so either I didn't "properly" reset the unit, or somehow the circuit board is able to detect the faulty dosing pump, or I also have a faulty circuit board too (unlikely):

I am going to order a new dosing pump, and take my board to Sure marine and (hopefully) they can bench test it.

The saga continues...
 
Mar 11, 2015
357
Hunter 33.5 Tacoma, WA
Sure Marine will not bench test the board. You have to take in the whole unit, which means disconnecting the water lines and exhaust. Since I knew other components were OK, I thought it silly to remove the entire unit.

The issue was not the dosing pump (the "thunking" was normal). It was the electronic control module (ECU). Odd, you can't purchase a ECU from Webasto separately, you have to purchase the entire combustion module as one unit. Also, there are differences between ECUs. Some control the water pump, some do not, some are for just diesel or gas, some (aftermarket) can be used for both. Webasto units are real big in Europe, and there seems to be way more parts/support available vice the USA.

In the end, I purchased an ECU off of ebay and now my system works properly. I learned a lot about my Webasto Top C unit, and I'm confident that I'd be able to quickly troubleshoot/repair any future issues myself.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Great write up of your project problem solved and resources to help other Webasto owners.
Thank you.
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
In the end, I purchased an ECU
Good work. I had the same issue with our fridge before we set off on our trip up north. I found a replacement ECU in Santa Cruz, CA when I was in San Francisco. Troubleshooting is half the game. The other 2/3rds (!) is finding the danged part.
Thanks for sharing. Congratulations.