Central heating misery (or mystery)!!

[3ndlessdreamz]

Hi hope somebody can help! We've had our open system boiler upgraded to a Viessmann Vitodens 050 combi back in August last year. When we had the heating on the first time in November when the thermostat was set to 20℃. After giving birth and having parents coming from the far east to help out, we needed a warm house, and everything was fine and dandy.
However the nightmare started when my parents left and we turned the thermostat down to 18℃ and the system was allowed to cool between fire ups, and we've had to top the pressure up twice a day!
We've had a local heating engineer checked all the radiators and valves and they weren't leaking. The company that installed the boiler checked the boiler and it isn't leaking. So we isolated the boiler and it wasn't the boiler, the pressure dropped from 1 to 0.2 bar when we opened the CH valves back up.
The only time we seem to have a drop in pressure is when the CH is cooling or cold, because I've literally topped up the pressure and had the heating on for 5 hours and no drop in pressure. And there are no damp patches on the ceiling anywhere. Any ideas?

 

[muggles]

Do you have any pipework under the floors downstairs? That would be a good place to start

 

[3ndlessdreamz]

Do you have any pipework under the floors downstairs? That would be a good place to start

That's what the installer and heating engineer both think, just the hassle I suppose!
But what I don't understand is why is the pressure dropping when it's cold and not when it's hot??? Surely if I have a leak it'll leak even when it's hot???

 

[muggles]

That's just how it is sometimes. Things expand and contract as they heat and cool

 

[45yearsagasman]

Pressure vessel been checked?

 

[3ndlessdreamz]

Pressure vessel been checked?

Not sure, but the PRV was dry when the installer came to check yesterday...Also the pressure didn't drop when the boiler was isolated

 

[wwwebber]

Pressure whilst hot and running should be approx 2 bar, then dropping to approx 1 bar when cold. What are you seeing that is different ?

 

[3ndlessdreamz]

Pressure whilst hot and running should be approx 2 bar, then dropping to approx 1 bar when cold. What are you seeing that is different ?

The pressure doesn't rise more than 0.2 bar when it's hot, and when it's at 1 bar it can stay like that for a very long time until suddenly it'll just start dropping at 0.2 bar per hour usually middle of night or early morning