Hidden toilet cisterns: pros, cons and what to plan

How a hidden cistern works

The cistern is a slim plastic tank fitted behind a false wall or inside a unit, usually above the pan. The fill valve and flush valve are inside it, as on any toilet, and the flush plate on the wall operates the flush valve through push rods, cables or a pneumatic link. On most designs, taking the plate off exposes an opening big enough to reach the valves and the isolation valve.

There are two common arrangements. With a wall-hung toilet, the cistern is built into a steel frame that also carries the weight of the pan, so the pan floats clear of the floor. With a back-to-wall toilet, the pan stands on the floor against a duct panel or piece of furniture, and a separate concealed cistern sits behind it.

The advantages

Most people choose a hidden cistern for the look. Without a visible tank the toilet takes up less visual space, and the wall above can be tiled, shelved or used for a recess. A wall-hung pan also leaves the floor clear underneath, which makes cleaning easier and helps a small bathroom feel larger.

• Cleaner, more modern appearance with fewer surfaces to clean
• Wall-hung pans leave the floor clear and can be set at a chosen height
• The duct or frame can hide pipework, including the soil connection
• Flush plates come in many finishes and can often be fitted at the top or front
• The boxing can double as a shelf or ledge

The disadvantages

The main drawback is access. If the fill valve starts letting by or the flush valve seal wears, the repair is done through the flush plate opening. That is usually fine, but only if the cistern was installed so the opening lines up and nothing blocks it. If the isolation valve is outside the reachable area, or the wrong product was used, a simple repair can mean opening up tiling.

Parts are specific to the manufacturer and sometimes to the model and year. A close-coupled cistern takes a wide range of universal parts; a concealed cistern often does not. A lesser-known brand can leave you hunting for a matching valve years later.

Faults are also less visible. A cistern that keeps running discharges into the pan through its internal overflow, so the only sign may be a constant trickle in the bowl or a water bill that creeps up. A leak inside the boxing can go unnoticed until it shows as a stain or a loose tile.

Frame, back-to-wall or close-coupled: which suits you

The right choice depends on the wall, the space and how much building work you are prepared to do.

Space and structure

A concealed cistern needs a duct or false wall deep enough to take the cistern, the frame if there is one, and the soil pipe connection. That depth comes out of the room, so check the manufacturer's installation drawing before committing to a layout. In a narrow London bathroom, the extra depth can decide whether the door still clears the pan.

A wall-hung frame must be fixed as the manufacturer specifies, usually to the floor and the wall behind. Timber floors, stud walls and old lath and plaster may need extra support. The pan is only as secure as the frame, so this is not a step to improvise.

Decisions to make before the wall is tiled

Almost every problem with hidden cisterns comes from decisions made before the room is finished. Once tiles are on, the options narrow.

• Choose a brand whose spare parts are widely stocked, and keep the model and installation leaflet
• Check the isolation valve can be reached and turned through the flush plate opening
• Line up the tiling so the flush plate opening is not obstructed by a tile joint or trim
• Fill, flush and check every joint for leaks before the boxing is closed
• Consider an access panel in the boxing if the soil connection or supply joints sit outside the plate opening
• Set the flush volume to suit the pan, within the water regulations limit

New toilets must meet the water fittings regulations on flush volume. For a dual flush, the full flush is limited to 6 litres, so a concealed cistern should be set up for the pan it serves.

Repairs when something goes wrong

Most concealed cistern faults are the same as on any toilet: a fill valve that will not shut off, a flush valve seal that lets water trickle into the pan, or a flush that does not activate because a push rod or cable has slipped. With the right parts and a clear opening, these are usually repaired without disturbing the wall. Our guide to repairing a concealed cistern through its service opening explains what can normally be reached.

If you are replacing an existing close-coupled toilet with a concealed one, the soil pipe position often decides how easy the change is. Our guide to choosing a toilet that fits the soil connection covers that part.

Planning a new toilet or bathroom

Loyal Plumbers plans and fits bathroom plumbing across London and inside the M25, including concealed cisterns, wall-hung toilets and the supply and waste connections behind them. We check the duct depth, frame fixing and access before anything is boxed in, so later repairs can be made through the opening rather than through the tiles.

Call us or send an enquiry with the product you have in mind, a photo of the current toilet position and whether the room is being fully refurbished.