Boiler keeps heating despite water being shut off

[Janiss]

Hi!
I have an anusual issue with my gas boiler Viessmann Vitodens 100.
When I open hot water, the boiler fires up and starts heating the water. However, when I shut the water off, the boiler seems not to understand that there water tap is closed and it just keeps heating till it gets to 90 degrees Celsius and only then shuts off.
I have had technicians coming and changing the little black part, which is supposed to recognize the water flow, but that does not help.
Also, tried changing the mother board - also did not help.
The weirdest thing is that, if you unplug the little black part and then plug it back, it will work for a little while but then go back to not working again.

 

[Deleted member 120897]

Sounds like the sensor is still moving.

Do you have any dripping taps? The technician’s, do they work for Veissmann? Have you got any other issues, such as a pressure increase?

 

[oz-plumber]

Pre-Heat function programmed into PCB?
Some brands of boilers keep the water hot in the DHW heat exchanger for an hour after last use of hot water.
It can be programmed out of the settings on some boilers

 

[Deleted member 120897]

Pre-Heat function programmed into PCB?
Some brands of boilers keep the water hot in the DHW heat exchanger for an hour after last use of hot water.
It can be programmed out of the settings on some boilers

Wouldn’t have thought the temperature would get to 90 degrees though unless bypassing into heating system.

 

[Janiss]

No, all the taps are shut, no water dripping anywhere.
Pressure is stable - does not increase or decrease really, so no other issues.

Yes, the technicians are authorized viessmann service provider.

They were guessing that maybe the issue isnt in the boiler, but somewhere in plumbing, however all the taps are closed, nothing is dripping etc., so cant really be that water is going elsewhere.

Sounds like the sensor is still moving.

Do you have any dripping taps? The technician’s, do they work for Veissmann? Have you got any other issues, such as a pressure increase?

 

[ShaunCorbs]

What filling loop do you have the one mounted on the cold water valve ?

 

[Janiss]

Omg, thank you
I have a filling loop with 2 valves and one of them(the one that is closest to the boiler) was left open.
I closed it and now the problem seems to have gone away. I hope it stays that way, but for now seems that that was the issue.

Cant believe that I was dealing with this for half a year and none of the technicians thought of this