Do i need my indirect water tank on?

tux900

markin said:

as the is an Indirect unvented hot water cylinder It must be a system

Actually, if you’ll forgive the pedantry of describing what is arguably an edge case, there’s nothing stopping you using a combi with an unvented cylinder if you disconnect the mains inlet and DHW outlet and instead use external valves to divert the primary circuit output to the CH and DHW as required. Whilst not all that commonplace it is sometimes done when properties are extended to include additional wet rooms that exceed the capacity of the pre-existing combi boiler but without having the (unnecessary) expense of replacing the boiler as well as adding the cylinder. To be fair though, I would concede that this makes it no longer a combi despite that being what the label might still say!