Viessman Vitodens 100-w pressure loss (no leak!)

[bulutug]

I have a Viessman Vitodens 100-w which keeps losing pressure even when the device is completely turned off.

If I top it up to 1 bar pressure, within about 20 mins it goes down to 0.5 bar and stabilises at that level.

There is no sign of water leak anywhere in or around the boiler or the house. We checked all the radiators and hidden places where the pipes go.

What could be causing this?
If the PRV is broken, would it be leaking out even at just 1 bar and even when the device is off?
We couldn't identify the root cause of the problem. Please help !

 

[terryplumb]

You have a leak ,either on the system ,or the boiler. Any water dripping from the pressure relief pipe outside ?

 

[bulutug]

You have a leak ,either on the system ,or the boiler. Any water dripping from the pressure relief pipe outside ?

not more than a few drops outside (which I guess wouldn't cause such a fast drop in pressure)
and we can't see any leak in the house anywhere

ALSO
if I run the boiler as normal, the pressure goes up to 3.5-4 level...
I'm wondering if the expansion vessel broke down first and then that led to PRV breakdown.. I don't know.. But now the pressure goes down even when the boiler is off - so I doubt it is expansion vessel related no?

 

[terryplumb]

If it constantly drips it would drop pressure. Tie a bag tightly around the PRV pipe to see how much it collects.

 

[bulutug]

If it constantly drips it would drop pressure. Tie a bag tightly around the PRV pipe to see how much it collects.

it is outside and approx 8m high above the ground. I can't quite see it. maybe I can put a bucket down somewhere..

 

[terryplumb]

If the pressure rises to around 3 bar when heating is in use ,then you certainly do have an issue with the expansion vessel. That in turn would likely cause the PRV not to fully close.

 

[Harry Bloomfield]

it is outside and approx 8m high above the ground. I can't quite see it. maybe I can put a bucket down somewhere..

That will not catch it. It needs a plastic bag, tapped over it or held with an elastic band to catch it. Also check if the condensate drain is dripping long after the boiler stops running.

 

[bulutug]

That will not catch it. It needs a plastic bag, tapped over it or held with an elastic band to catch it. Also check if the condensate drain is dripping long after the boiler stops running.

I don't have a ladder that high - and even if I had one I would be scared at 8m to be frank
How do I check the condensate drain? that goes into a pipe. I would need to undo that somehow..

 

[Harry Bloomfield]

I don't have a ladder that high - and even if I had one I would be scared at 8m to be frank
How do I check the condensate drain? that goes into a pipe. I would need to undo that somehow..

Look at the end of the pipe, where ever it drains..