Pressure keeps rising

[Peter_1974]

Hi Pros,

I have an interesting issue with my heater, I hope one of you will know the reason. (It's a Vaillant vuw 202/3-5)

Almost everything is ok, it heats and makes hot water. But the pressure keeps rising. 0,1 bar every 2-3 hours. I have already replaced the filling valve but didn't help.
I have no idea what to check or change...

All suggestions are very welcome!
Thanks in advance,
Peter

 

[GReynolds929]

Has the thermal expansion tank been checked or replaced?

 

[Peter_1974]

Hi GReynolds929,

No, it hasn't been replaced, nor checked, because I don't know how damage to the tank could cause this. If I close the water (before the heater) the pressure doesn't rise. So I think the water comes from the water supply somehow.