Webasto Termo Top Not Working? Troubleshooting.

Hello.

I have a question about the Termo Top, maybe someone can help:

I tested the heater before installation to make sure it worked. I connected the starter cable to the positive and negative terminals, filled the fuel tank, placed a bucket of water nearby, and plugged in a clock... and the heater is running.

Now that it's installed, absolutely nothing is happening.

Wenn ich die Uhr einschalte, klickt das Relais für das Gebläse kurz, ca. 1 sek. Ich höre etwas in der Heizung anlaufen, weiss aber nicht, ob das die Wasserpupe oder der Verbrennungsluftmotor ist. MeIt won't happen.

Good advice comes at a price.

Who can help?

Thank you in advance. Best regards, Thommi.

Hi,
The Thermo Top is capable of diagnostics: it has a search function. If you are unable to do this yourself, you should have the data read out by another source, such as a Bosch service center.

Hello.

You're right, it's also mentioned in the operating manual. However, for that to work, the device needs to be running, and in my case, the error code can be read using a blinking sequence.

It's not possible with the laptop; it's too old for that.

By the way, I already had someone from Bosch come out, and they said the problem is likely due to corroded connections on the heating unit, which is causing a voltage drop.

Also Stosstange zum 3. Let's see...

Best regards, Thommi.

Hello.


Further up, I described the problems I was experiencing, and it turned out that the control unit was defective.

'This item is not sold separately; it's only available in conjunction with the heat exchanger. The price is €185 plus VAT. Webasto cites sealing problems and changes in sealing materials as the reason for this measure. All heat exchangers are thoroughly tested for leaks using a control unit.'

At the same time, there is the option to send the heating unit in for repair, in which case only the control unit is replaced and the previously mentioned tests are carried out. However, this also costs €150.

I managed to get ahold of one of those parts individually. I'll build it later and let you know if you're interested.

Best regards, Thommi.

Hello.

As described above, I installed the control unit yesterday.

First, regarding the type of heater: It's an 'older' Termo Top model, which cannot be diagnosed via laptop, and it has the 'old' connector that is not waterproof. The newer heaters can be identified by their waterproof connectors.

After I had removed the bumper for the 5th time, , I temporarily connected the control unit without attaching it firmly to the heat sink. I turned on the heater, and it started immediately.

After about 30 seconds, the combustion air blower started running very slowly and then stopped completely. Hmm, at that point, finding a solution was going to be quite expensive...

Using the voltmeter, I discovered that there is also full voltage on the ground side, which indicates a clear grounding problem (?). But how does the thermal regulation work when the device gets warm?

Quite by chance, while measuring and handling components, I came into contact with one of the constant voltage regulators (or similar components), of which there are three on the circuit board. One of them was so hot that I burned my fingers.

Somehow, I then realized that the problem might be located there.

I then pushed the control unit against the heat exchanger, and the retaining clips were positioned against the heat exchanger. The clips are used to press the retaining clips against the heat exchanger.

And lo, the heater started up without any problems, as if nothing had ever happened.
The warming-up procedure was initiated.

I made another attempt by applying thermal paste to the back of the retaining clips and then turning on the device. It still wouldn't start; during the heating and ignition phase, the combustion air blower was already running too fast, at full speed as if it were in the afterburn mode.

If the 'insulating paper' is missing behind the thermostat, the control system will activate too early, meaning the device will only heat the water to 60°C (measured digitally).

The system operates through the electronic components, which are connected to resistors that change their resistance based on temperature. When the heating element is heated by the water, the cooling mechanism also changes, which alters the resistance and, consequently, the voltage or current flow to ground.

After that, I removed the control unit again, replaced the gasket, applied a small amount of sealant, put everything back in place, tightened the screws, and I hope it's sealed now. We'll see if that's the case later.

Several test runs yesterday were successful.

This morning, the heating device started up immediately, regulated itself, and continued running as it should.

Best regards, Thommi.