Blow out valve question

[happypig]

My CH system has an expansion vessel and on top is a pressure gauge and a blowout valve with a spring loaded manual knob (ie open the valve and it lets a bit of pressure out).
Can anyone advise, does the valve let out all the time it's open, or does it only let out until a certain pressure is reached ?

 

[wannocks]

It's probably a pressure relief valve. It will be open for as long as you hold it open, under normal operation it will open at 3bar.
You shouldn't play with it or use it to drain the system, if it gets dirt in the seat it will leak and your system will keep loosing pressure.

 

[theheatinghelper]

well said that man !!!

 

[happypig]

Thanks for the info.
CH is at higher pressure than it should be so I was just letting a bit out.
I think I might have let too much in when I changed a rad last week.
the valve I have is spring loaded and when I turn it, it releses a bit of pressure then "clicks" and shuts and the heating hammers for a few seconds.
Got a feller coming to service the boiler soon so I will get him to check it.

 

[MANDATE]

You can check it yourself. It will discharge outside somewhere and if not properly seated it will leak and your pressure will drop.
Next time you want to reduce pressure just bleed a radiator