Webasto STH: Starts only after reset!

Hello everyone,

I'm having a problem with my STH Thermo Top C diesel heater.
When I start the STH (whether with the control panel or at the pre-selection unit), it does turn on, but it doesn't start heating. I've noticed that the metering pump isn't cycling, so no diesel is being pumped. If I start the STH by bypassing the fault protection (by pulling out the 20A fuse for 30 seconds, then reinserting it, turning on the STH, waiting 3 seconds, removing the fuse again for 3 seconds, and then reinserting it), the metering pump starts cycling, and the heating works perfectly.
So, the dosing pump isn't defective; I actually replaced it just 6 months ago.
I suspect it might be a problem with the control unit. Is it possible to identify this error using a diagnostic tool, or can anyone offer me some advice?
Thank you.

Regards,
Alfajunkie

However, it's also possible that the pump is stuck and that your troubleshooting procedure 'unclogs' it.

-> www.webasto.de
Hotline: 01805 - 707 400 (12 cents per minute).


CU Gremlin.

@ Gremlin

Hello,

and thank you for the answer.
I don't think the pump is clogged.
I have now gained more experience with STH.
On the first attempt to start the STH normally, one day after I had managed to get it running again using the anti-interference lock, it worked as usual. The STH started up, but there was no burning. After about 3 minutes, it automatically peeled off. I tried this three times within 6 hours. And sure enough, on the third attempt, it worked. The STH ran for 30 minutes.
One day later, the first attempt also failed. It automatically stopped after about 3 minutes. The second attempt, about 6 hours later, was successful.
I suspect that after a longer period of inactivity, the duration until the fuel is delivered to the engine is too long, or there is air in the line. I believe this is particularly related to the fuel intake. The fuel is currently being drawn through a T-fitting in the return line. This is also confirmed by the opinion of a knowledgeable person who has installed many such systems. He believes that drawing fuel through a T-fitting is not ideal and recommends taking it directly from the fuel tank line. I will try to install this in the next few days (week) and then we'll see what happens.

Regards,
Alfajunkie

I had similar problems with my heating system as you did.

I almost went crazy trying to find the error.
It could also be due to several factors, just like it was in my case before.

- Heater not properly bled (on the coolant side).
- Low voltage at the unit.
- Incorrect detection of operating status. For example, 'device on/off,' etc.
or, as you may have already suspected, a lack of fuel supply.


Okay, a general diagnosis of a ZH (heating system) or ZSH (heated seat) can only be performed if the STH (sensor/control unit) is connected to the vehicle's bus system. Otherwise, perhaps directly from Webasto?

Specifically, I believe it's due to the decrease in fuel. Namely, the fluid is tapped off via a T-piece in the return line.

AARRGGHH

That's going to fail. If it's done at all, the fuel must be taken from the supply line *before* the filter (NOT in systems with an electric pre-pump like PD or CR -> requires a separate fuel tank tap!).
'It should be placed before the filter because the small heating pump might not be able to draw fuel through the filter in the winter (especially if it's heavily clogged), and it could then drain the fuel injection pump backwards. Ideally, a separate fuel pickup would be used.'
'If you draw water from the return line, the heating system will naturally only suck in air because the return line ends somewhere in the tank, but with a very high probability, not below the liquid level.'

By the way, this is also mentioned in the installation instructions!

CU Gremlin.

@gremlin
THIS will go wrong. If at all, the fuel must be taken from the tank BEFORE the filter (NOT in systems with an electric pre-injection pump like PD or CR -> separate tank extraction!).


Hello,

Since I have a CR-Diesel engine, it's likely that both issues are relevant. Therefore, I definitely need to install a fuel level sensor.
Thank you for the tips.

Regards,
Alfajunkie.

As soon as the fuel tank sensor is installed, I will share my experiences.

Hi.

@ Alfajunkie:
What is this "de-interference unlock" mode that you are describing ? I tried it, but there is absolutely no difference. Are there any other tricks?
If the problem for you was the excessively long fuel line, then the metering pump should have still been ticking. But you said it wasn't ticking, right?

I was so foolish and also bought a Webasto Termo Top C on eBay. This thing turns on the fan and then stops the air blowing after two minutes. It doesn't even attempt to ignite, and it doesn't even try to draw diesel.
I've checked everything (the dosing pump works manually, the glow plug glows [when connected directly to the battery], the fan blows). There's also voltage at the pump during the two minutes (it looks like PWM with a low duty cycle, but I only had a multimeter available), but no diesel is being pumped. The heater should definitely be supplying voltage to the glow plug first.

All Webasto units are self-diagnosing. So, it's best to take it to a Bosch service center, offer them a 5-euro tip for the coffee fund, and have them read the error codes.

The water pump starts immediately upon ignition, and the combustion air blower is briefly run at full speed. The glow plug heats up, and then, after about a minute, the combustion air blower slowly starts up, and fuel delivery begins.

Have you checked everything for smooth operation? Are the temperature sensors working correctly? Is the flame sensor working properly?
btw: you always have to test the components inside the heating system. For example, the fact that the glow plug glows at the battery } doesn't necessarily mean that it's getting enough power in the heating system.

Otherwise: I've already posted this a thousand times. Webasto and Eberspächer have hotlines and email services, and they are really very good!

CU Gremlin.

@Jan03

'Quote from Webasto operating instructions regarding troubleshooting and unlocking.'
'In the event of a malfunction, the heating device enters a fault-lock state, and no error message is displayed on the clock's screen.'

The fault clearing process works as follows:
Remove the 20A fuse (yellow) -> wait 3 seconds -> reinsert the fuse -> turn on the device at the clock or transmitter -> wait 3 seconds -> remove the fuse again -> wait 3 seconds -> reinsert the fuse.
'The starter heating system (SHS) activated, and the dosing pump started cycling. However, when I turned the SHS back on one day later, it didn't work again. I think it takes too long for the diesel to reach the combustion chamber. To prevent damage, the SHS then goes into a fault lock (due to overheating of the glow plug!).'

Before I continue experimenting here, I'm going to follow Gremlin's suggestion first (thanks). Unfortunately, I haven't been able to acquire any fuel tank senders yet.
I hope my friend brings one over to me by Saturday. He seems to have a few lying around in his garage.
It's getting cold lately (although I have a garage, a pre-warmed car is very pleasant and environmentally friendly ).

Das mit der freundlichen Hotline bei Webasto kann ich bestätigen. Die haben mir ohne viel aufsehen eine Betriebsanleitung für meine STH zugefaxt. NPlease be polite.

If you like, I can send them to you.
I also have the original Data-Top CD from Webasto. However, it's not that great. It contains some information about the functions, wiring diagrams, and so on. But it didn't really help me much.

Greetings.

Alfajunkie.


I've written a lot, haha.

@Alfajunkie

What kind of auxiliary heater do you have? Is it a Thermo Top?

"According to CD, Webasto may have made a change, adding a capacitor to the water pump line, because there were "self-oscillations" in the control unit. The capacitor was intended to prevent this."

Best regards,
Eric

When the heating device is switched on at temperatures...
Below +5°C, inadmissible self-oscillations may occur in the...
Control unit may occur. In this case, the system will switch off.
Immediately switch the heating device to afterflow mode.

It's in the Webasto workshop manual.

hello kini,

Okay, I have a Thermo Top C. I'm not aware of any issues with a capacitor, but since the fuel pump isn't running even at temperatures above 5°C, I don't think that's the problem. As I mentioned before, after the second or third start, the fuel pump usually works fine. Unfortunately, I haven't been able to install the fuel level sensor yet. I hope to get to it soon and will let you know if it helps.

I also have a Webasto CD from 2001. Where exactly is the information about the capacitor located?
Regards,
Alfajunkie

hi

Have you already read the error codes?

The capacitor is only used with the Thermotop, not with the Thermotop C.

Best regards,
Eric

Okay, I just remembered something. Did you connect the switch for summer mode? If so, maybe there's a problem with it. It's connected to pin 5 of connector X1. If that pin is connected to ground, the heating won't work, and it will only ventilate.

hello,

After finally having time during the Christmas holidays to install the fuel tank sender, I would now like to say, after a good 14-day testing period, that it works .
Now the STH starts up and runs properly at any time.

I hope I haven't gotten my hopes up too soon.

Regards,
Alfajunkie

Great feedback!

Hi,

Well, another year has gone by.
Unfortunately, the solution with the fuel pump didn't work. It was actually similar to the previous problem. Whether the engine would start and run through the self-test sequence depended on chance.
Since I, like almost every year, have a lot of free time during the holidays, I have now expanded the STH.
After removing the combustion chamber, I noticed large, black chunks inside. I removed as many of these as possible. I also cleaned everything around the glow plug.
As I've read in this forum, the felt material in the burner, which is located in front of the glow plug/flame sensor, can also be a cause of irregularities in the burner operation.
As far as I can tell, my filter looks fine. It's not burned through or incomplete anywhere. The distance to the glow plug is also correct. It only has a small amount of carbon buildup.

I also called the Webasto hotline and casually inquired whether there were any known issues with combustion chambers and non-woven materials, but I only received a vague answer. I was then referred to a Webasto partner.
I also inquired there, and I was told that the sunroof heating (STH) usually functions without problems for 5-6 years, after which the dealer sends it to Webasto for repair or refurbishment.
He couldn't offer me just the combustion chamber; it's only available as a complete unit with the housing for €170 + a 'fairy tale tax.'

For testing purposes, I have now reinstalled the cleaned combustion chamber (using old seals; once I know what the problem is, I will use the new seals I already have). During the first test run, the heating system started up and burned cleanly, but it didn't complete the cycle. I suspect that the system detected a temperature limit due to air in the cooling system and therefore triggered an error (the water hoses to and from the heat exchanger were completely empty, even though the circulation pump was clearly audible; it's unlikely that the circulation pump has failed, right?).
After that, I brought the engine up to operating temperature to ensure that the cooling system was properly bled. I will then attempt another start tomorrow.

Okay, now for my questions:
-What should the burner fleece look like? (Unfortunately, I don't have a digital camera, otherwise I would have included some pictures.)
-Is it sufficient to simply remove the residues?
-How exactly does the fuel ignite? Is the fuel injected into the fiber material, atomized, and then ignited, or does the fuel simply flow through the fiber material normally?
-Where can I get a replacement burner chamber, besides from eBay?

Okay, that's enough for now.

Hello.
Alfajunkie

Hi there,

I'm still experiencing the same problem. Initially, it seemed to be working well; during the first 5 test runs, within 4 days, the engine started up perfectly and ran smoothly. However, after I disassembled the combustion chamber again to replace the seals, and then tried to start it about 3 days after reassembly, it wouldn't start. But after releasing the anti-tamper lock, it started up and ran normally again!
I probably need a new combustion chamber, or maybe the problem is even with the control unit.
Okay, when I have some time and don't need the car, I'll probably connect a diagnostic tool to it.

What I found somewhat surprising, however, were renewed deposits of oil and soot in the combustion chamber, and that after only 5 uses! So much for the claim of being maintenance-free .
Can someone tell me how to adjust the CO (carbon monoxide) level? Is a diagnostic tool required for this?

Hello.
Alfajunkie