Cistern

A cistern holds and releases the flush water. Most toilets are sold as a pan and cistern together, but cisterns are also bought separately — either to replace a failed one, or because the pan you want is supplied on its own.

Close coupled or concealed?

Close coupled cisterns bolt directly onto the back of the pan and are visible. Simple to fit, simple to service. Concealed cisterns sit inside a WC unit or a wall frame, operated by a flush plate.

Matching a replacement

Cisterns are not universal. If you are replacing one, match the make and model of the pan wherever possible — the bolt spacing, the outlet position and the seal all have to line up. Where the original is discontinued, a universal cistern may fit, but check the fixing centres against your pan first.

Dual flush

Almost all modern cisterns are dual flush, typically 6 litres full and 3 or 4 litres reduced. Over a year that is a meaningful saving on a metered supply.

Fittings

Check whether the cistern includes the inlet valve, flush valve and push button, or whether those are separate. It varies by manufacturer and is easy to get caught out on.