Replacing a toilet cistern fill and flush valve yourself

What to check before going to the shop

Take the lid off the cistern and look at what you actually have. There are two separate mechanisms: the fill valve (the tall unit connected to the water supply pipe, which refills the tank) and the flush valve (the wider unit in the middle, with the flap or seal that drops when you press the button). A running cistern can be caused by either one, so confirm which is faulty before buying a part.

Note the cistern's shape and the position of the outlet at the bottom, because flush valves come in different heights and overflow-pipe positions. Measure the distance from the base of the tank to the water line, and check whether your toilet uses a two-button dual flush or a single lever, since the mechanisms are not interchangeable.

Also check the connection at the bottom of the cistern where the angle valve meets the fill valve. Most flats in Tallinn use a 3/8 inch (roughly 10 mm) threaded connection, but older Soviet-era panel buildings sometimes have different fittings, so it helps to unscrew the flexible hose end and take it with you when buying a replacement.

Tools and materials you will need

This job needs very little specialist equipment, which is part of why it is worth doing yourself if you are reasonably confident with a spanner. Buy a universal fill valve and a universal flush valve if your cistern is a standard shape; these adjust to fit most tank heights and outlet sizes.

Have a bucket, an old towel and a sponge ready, since there will always be some water left in the cistern and pipe even after shutting the supply. A small torch is useful for seeing the nut underneath the cistern in a dark cabinet or boxed-in area.

• Universal fill valve and flush valve (matched to your cistern's height and outlet)
• Adjustable spanner or slip-joint pliers
• Bucket, old towel, sponge
• PTFE tape (plumber's tape) for the threaded connections
• New flexible supply hose, if the old one is stiff or corroded
• Torch

How to shut off the water safely and drain the cistern

Find the angle valve on the pipe running into the cistern, usually just behind or beside the toilet, and turn it clockwise until it stops. If it will not turn, or turns but water still trickles into the tank, do not force it; a seized angle valve is a common reason this job goes wrong, and it is safer to shut the water off at the main stopcock for the flat instead.

Flush the toilet to empty as much water as possible, then hold the flap or button down to let the tank drain as low as it will go. Use the sponge to soak up what remains at the bottom, since you will be disconnecting fittings that sit below the water line.

Place the bucket and towel under the cistern before disconnecting anything. Even with the water off, the flexible hose and the nuts holding the mechanisms in place will hold a small amount of water that runs out as soon as you loosen them.

Removing the old mechanism and fitting the new one

Disconnect the flexible hose from the base of the fill valve, then undo the large plastic locknut underneath the cistern that holds the fill valve in place, turning it anticlockwise. Lift the old fill valve out from inside the tank. For the flush valve, undo the corresponding locknut on the outlet at the bottom, noting how the overflow pipe connects, since the new unit needs to replicate that link.

Fit the new flush valve first, since it usually needs the tank to be fully empty and gives you more room to work. Seat the rubber washer correctly against the base of the tank before tightening the locknut by hand, then a quarter-turn further with pliers; overtightening is the single most common mistake here, and it cracks the plastic thread or the base of the cistern.

Fit the new fill valve the same way, wrapping the threaded tail in two or three turns of PTFE tape before screwing the locknut on. Adjust the float or the height setting on the fill valve to match your old water line, usually marked inside the tank or roughly 2 centimetres below the top of the overflow pipe.

Reconnecting the water and testing

Reconnect the flexible hose to the fill valve by hand first, then tighten with a spanner until snug, without overdoing it, plastic threads can strip. Open the angle valve slowly and watch both connections underneath the cistern for drips while the tank fills.

Once the tank has filled, flush it fully and watch the flush valve seat itself properly and stop the water at the correct level. Do this two or three times, checking for leaks at the base each time, since a slow drip sometimes only appears after the joint has settled under pressure.

Leave the cistern lid off for ten to fifteen minutes and check again before considering the job finished. If everything holds and the fill stops cleanly, put the lid back on.

When to leave the job to a plumber

If the angle valve will not shut, or the fittings underneath are corroded and won't turn, stop rather than force anything with a spanner; a stripped or snapped fitting on a live supply line usually means a much bigger repair. This is also the point at which the flat's stopcock or a shut-off for the whole building may need to be used, which is easier for someone who does this regularly.

Cisterns built into a wall (concealed cisterns) are a different job entirely, since the mechanism sits behind tiling or a panel and often needs different tools to access. If your toilet is one of these, or if you are not confident matching threads and adjusting float heights, it is worth having it done properly rather than risking a leak inside a wall.

Toilet repair and fitting is available from 60 € per job, and general plumbing work from 45 € per hour, with a fixed quote given in advance for anything beyond a straightforward valve swap.