Webasto Water Pump Troubleshooting

Hi everyone!

After my father had been complaining for a while about the lack of heating power from his Webasto Thermo Top C, I decided to take a look at it today.
So, I immediately connected the diagnostic tool and started the heating system. The water temperature rose rapidly (approximately 1°C per second). Furthermore, the water pump made no noise, not even during the component test of the diagnostic tool.
Apparently, there's a defect with the water pump.

Then I opened the cover of the pump and was quite surprised. The water pump has the stator winding inside and a permanent magnet rotor on the outside, to which the pump blades are attached. The advantage of this design is that the motor is absolutely waterproof. The major disadvantage is that the pump impeller is magnetic, which means that all magnetic parts in the water will be attracted to it.
And that was exactly the problem. The wheel was very difficult to turn.
The wheel is secured with a retaining ring and can be easily removed.

I then cleaned everything thoroughly, and the heating system is working like new again.

Unfortunately, the diagnostic tool only displays the target value, not the actual value, of the water pump. Therefore, you have to rely on your hearing.

So, anyone who is installing a used heating system or who has just removed their heating system for repairs should take a look at the pump.