Hot water cylinder All aspects of plumbing questions and answers, help, tips and information

[cuban8]

Hi.

Can anyone explain why there is a small pipe with a stop valve between the input and outlet points (to the heating coil) on our central heating's hot water cylinder. Haven't seen this on diagrams of central heating.... some sort of bypass? How should it be set?

Thanks

C8

[bobplum]

assuming it is a gravity system there should be a pipe coming down from the cold water tank in the loft and entering the hot water cylinder at the bottom on this pipe there should be a gate vale,usually red and circular turn this clockwise it will stop the flow of water into the hot tank and stop the flow of hot water thru the taps

[badger]

I'm no heating engineer, but I had the same question myself a few days ago...
So far as I can tell it's there because your pump is powerful enough to create decent flow through all your radiators. When the CH is off the pump would be exerting too much pressure on the relatively light load of the cylinder coil and could well start to push hot water up the vent (gravity system).
The bypass prevents this and has a valve that can be adjusted to regulate the amount of bypass. ie, if the outlet from the coil is pretty much the same temperature as the input, and the tank is heating up fine, there's enough flow through it.

If all that is baloney, no doubt someone will step in and tell us!