Viessman Vitodens 100-w pressure problem

[terryplumb]

Your systems pressure relief valve
(PRV) should open at 3 bar ,and water should come out of that pipe outside. If the expansion vessel is functioning correctly ,your system pressure shouldn't get to 3 bar in the first place . Your pipes and radiators etc can cope with more than 3 bar.

 

[coltmanneil]

I have an older Viessman vitodens 100-w wb1b 30kw install 2011. When we first got it and it still does it now when in stand-by it goes down to 0.2bar pressure. When it was new I topped the pressure up thinking there was a problem with it . Of course soon as the boiler heating came on the pressure rose to 2.9 . The installer said I shoiuldnt have topped it up as it didnt work the same way as my previous vokera boiler where the stanby pressure was constant 1.5bar. This Viessman stand-by pressure drops right down , then when it comes on rises back to 1-1.5 bar. Lesson learnt here for me I now leave it alone. Seems like you have an over-pressure problem as you know. Hope you got it sorted.