How do I fix a Geberit concealed cistern that keeps running?

Geberit concealed cistern repair: how it is built

To fix a running or weak concealed cistern, work through the opening behind the flush plate. Take the plate off and find the fill valve, which lets water in, and the flush valve, which lets it out. Then work out which one is misbehaving before you buy anything.

GROHE says its concealed frames keep the cistern, drain and pipes hidden behind the wall, operated by a flush plate. It also says its powder-coated steel frames are TUV-approved to support up to 400 kg. That is GROHE's claim for its own frames, not a claim about every wall-hung toilet.

Geberit describes the same layout: the cistern sits behind the wall with a flush plate, or actuator plate, on the front, and each plate is matched to a cistern series. If you are still choosing a toilet for a BTO or condo renovation, see wall-hung vs floor toilet.

Concealed cistern leaking or running

A concealed cistern leaking into the bowl is easy to miss because there is no tank lid to lift. Look for a thin ripple at the back of the bowl, a faint hiss at night or a refill when nobody has flushed.

PUB suggests leak detection tablets. Drop one tablet into the cistern tank, put the lid back, wait 10 to 20 minutes without flushing and check the bowl. If the water turns blue, there is a leak, and PUB says to call a licensed plumber to fix or replace the flushing cistern. On a concealed unit, drop the tablet in through the plate opening and refit the plate. If you have no tablet, a few drops of food colouring work the same way.

If colour shows in the bowl, the flush valve seal is the likely cause. If the bowl water stays clear but the cistern keeps filling, look at the fill valve. HDB lists overflow fixes such as adjusting the water level screw. It also says to engage a plumber if your flushing system is different from its illustrations. For general steps, see toilet keeps running.

Weak flush

A weak flush usually means there is too little water in the cistern or the water arrives too slowly. Check three things:

• Fill level. If the water stops low in the cistern, the flush has less to push with.
• Stop valve. A stop valve left partly closed after renovation works also slows refilling.
• Scale. Mineral build-up can narrow the fill valve inlet and stiffen moving parts.

For causes outside the cistern, see toilet flush weak.

Geberit flush plate stuck

A button that stays pressed in, or one that clicks without flushing, usually points to the linkage. Behind the plate, actuators or rods pass the push of the button to the flush valve. If a rod has slipped, bent or been set to the wrong length, it can jam the button or miss the valve.

Dirt is the other usual suspect. In a well-used bathroom, soap residue, dust and grit build up around the button edges until the button drags.

Remove the plate slowly. Plates are held in different ways, and forcing one can crack the plate or snap a rod, so check the maker's instructions for your plate model first. Lay the plate face down on a towel and press each button. A wipe around the edges may free it. A broken rod or actuator needs the matching part.

Spare parts and model

Geberit says it keeps spare parts for its concealed cisterns available for 50 years, excluding some electronic components. It also says its flushing systems are tested with a minimum of 200,000 flushes and refills. Both are Geberit's own statements about its own products.

Long availability only helps if you order the right part. Identify the cistern series before you buy a fill valve, flush valve or plate, because a part made for one series may not fit another. If you bought a resale flat and the previous owner left no paperwork, start with photos of the opening and the back of the plate.

Quotes depend on the part and on how much access the job needs. The toilet cistern repair cost guide covers pricing.

When to call a plumber

Call a licensed plumber if water shows at the base of the wall, the grout near the toilet stays damp or stained, or you can hear a leak behind the tiles away from the plate opening. Moving the bowl is sanitary plumbing work, not a part swap.

PUB says all regulated water service and sanitary plumbing works must be done by PUB Licensed Plumbers, except the simple plumbing works handymen may do. Since 2018 it has been an offence to engage a plumber not licensed by PUB for regulated works. To see where that line sits, read what needs a licensed plumber.

To find help, browse companies offering toilet repair. Ask whether they work on concealed cisterns and can source parts for your series.

Questions