Correct expansion vessel pressure?

[psychopomp1]

Hi,
A few days I got my crappy Ideal boiler replaced by a Viessmann Vitodens 100 16kw boiler (heat only) and couldn't be happier....the Viessmann is super quiet (just a gentle hum) and it heats up water super fast.

I have a question regarding the external expansion vessels i have upstairs next to my hot water cyclinder. When the house was built in 2008, the builder said i should keep the pressure at 1.5 bars in the red expansion vessel and this has always been maintained, over the years any plumbers which have worked on my plumbing have agreed this pressure is about right. However the plumber who installed the Viessmann boiler set the pressure to 1 bar, when i asked him why he said the boiler installation instructions said the pressure should be set to 0.8 bars. What were to happen if i increased the pressure to 1.5 bars? Reason is that the taps seem to have slightly less pressure, would like to get my old flow rate back!

FYI i have a sealed, pressurised water system.

Cheers

 

[chris watkins]

Hi,
A few days I got my crappy Ideal boiler replaced by a Viessmann Vitodens 100 16kw boiler (heat only) and couldn't be happier....the Viessmann is super quiet (just a gentle hum) and it heats up water super fast. Good stuff, so have I

I have a question regarding the external expansion vessels i have upstairs next to my hot water cyclinder. When the house was built in 2008, the builder that was the problem the builder said said i should keep the pressure at 1.5 bars in the red expansion vessel and this has always been maintained, over the years any plumbers which have worked on my plumbing have agreed this pressure is about right. However the plumber who installed the Viessmann boiler set the pressure to 1 bar,1Bar is more than enough when i asked him why he said the boiler installation instructions said the pressure should be set to 0.8 bars. What were to happen if i increased the pressure to 1.5 bars? The heating expansion vessel will not be able to take up as much expansion in the system Reason is that the taps seem to have slightly less pressure, would like to get my old flow rate back! The charge pressure of the heating expansion vessel has absolute nothing to do with the cold or hot water pressure or flow rate, They are separate systems.

FYI i have a sealed, pressurised water system.

Cheers

Hi Please see bold text above.
The vessel pressure charge is determined by the static system head pressure above the vessel. Most systems & boilers require a minimum of 0.8 bar or 8Metres head of water in the system so 1 bar is normal in a two story house. 1.5bar especially on the top floor is too much IMHO but it does depend on the size of the vessel & its pre-charge pressure.
Hope that helps.

 

[Dotty]

So in a nutshell, it's been set correctly.

The pressure at your taps is unrelated. But check your stopcock under the sink has been opened fully.

 

[psychopomp1]

ok thanks guys, puts my mind at ease.