Hello good people of reddit, I’m hoping someone can help me with my boiler pressure problem.

This is a photo of my Viessmann Vitodens 100-W wall mounted gas condensing boiler. It’s five and a half years older and is connected to a unvented cylinder. For the last six months the pressure gauge has been showing zero/nil.

I had it serviced six months ago and my plumber filled the system with water. This didn’t fix the problem so he tried to put some air in the diaphragm expansion vessel with my bike pump (he said it was probably full of water). This didn’t fix the problem either. He told me he would contact Viessmann to see if it was covered by warranty. I doubt that it is at 5.5 years old and despite me chasing him infrequently I can’t get hold of him for a response / update / answer / remedy.

Is it fine or should I worry? I’m mindful that I have no idea how much pressure is in the system which possibly isn’t a good thing. For all I know the pressure could be rock bottom or sky high - I think the zero is a false reading.

Should I consider getting a new diaphragm extension vessel fitted?

Should I consider getting a new plumber?!

Thanks for helping me get to the bottom of this!