Hi eveares, the primary circuit is connected to the expansion vessel.
Generally CH systems are topped up to 1.5bar cold, unless stated otherwise in MI.
Can't comment on the hot water tap running.
The valve in your picture is a combination valve that does many things, one thing it can't do though is isolate the cylinder. Every cylinder should have a stop tap fitted nearby to isolate. The valve you shown also doesn't pressurize the cylinder, but restricts the flow to give a balanced hot and cold flow throughout the property.
Generally CH systems are topped up to 1.5bar cold, unless stated otherwise in MI.
Can't comment on the hot water tap running.
The valve in your picture is a combination valve that does many things, one thing it can't do though is isolate the cylinder. Every cylinder should have a stop tap fitted nearby to isolate. The valve you shown also doesn't pressurize the cylinder, but restricts the flow to give a balanced hot and cold flow throughout the property.