Cylinder question any help

[Nickwigan]

i was called out to a fault on a cylinder coil had failed that’s fine
But from pics some one has put a 3 port and zone valve on
both wired up so a bit confusing

 

[Deleted member 120897]

From what I’ve read previously, it’s a safety device for unvented cylinders, think it’s because 2 port is spring return.

Have a look here

 

[Chuck]

You see this done to satisfy BR G3 section 3.13 when a Y-plan vented system has the cylinder upgraded to an unvented one. It's neater to remove the three-port valve and convert to S-plan but that does add the cost of another 2-port valve.

 

[king of pipes]

Not unusual as Chris has said the 2 port is one of the safety devices supplied with a unvented cylinder, a 3 port always has one port open even when the heating and or hot water is satisfied, upgrade it when you replace the cylinder you will need to sort the discharge pipes out solvent weld pipework does not comply with building regulations? and mount the expansion vessels correctly I always fit timber or a piece of ply to the wall first as if they fail there heavy . Kop