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.

 

[GReynolds929]

When water is heated it expands and creates extra pressure. If the expansion tank is waterlogged or there isn't one the expanded water has nowhere to go increasing pressure in the system.