Toilet keeps running: it's almost always one of two parts
The Abimeister team · Updated · 5 min read
If your toilet cistern keeps refilling on its own, or you hear a hiss every few minutes even when nobody has used it, the cause is nearly always one of two parts inside the tank: the fill valve or the flush valve seal, often called the flapper. Both are cheap, both fail for ordinary reasons after years of use, and both are usually simple enough to check yourself before deciding whether to order a part or call someone in. This guide walks through telling the two apart, what you can do yourself, and what the running water is actually costing you.
What's the difference between the fill valve and the flush valve
The fill valve is the taller mechanism, usually on the left side of the cistern, connected to the water supply. Its job is to let water in after a flush and shut off once the tank reaches the right level, controlled by a float that rises with the water.
The flush valve sits at the bottom of the tank, in the middle, and is the large opening the water drains through when you flush. A rubber or silicone seal, the flapper, sits over this opening and is meant to close and hold water in the tank between flushes.
If the fill valve fails, water usually runs constantly or restarts every few minutes because it never fully shuts off. If the flush valve seal fails, water quietly seeps down through the bottom of the tank into the bowl, and the fill valve keeps topping it up to compensate, which sounds similar but has a different cause.
How to check quickly which part is faulty
Take the lid off the cistern and look at the water level. If it's above the overflow tube, or right at the top and still rising, the fill valve isn't shutting off properly. Lift the float gently by hand: if the water stops running the moment you do, the float or the fill valve mechanism is the problem.
If the water level looks normal and stops on its own, the leak is probably at the bottom. Add a few drops of food colouring to the tank water and wait ten minutes without flushing. If colour appears in the bowl, the flush valve seal isn't sealing and needs attention.
You can also just listen. A fill valve fault tends to hiss or trickle audibly and often continuously. A flush valve seal fault is quieter, sometimes only a faint sound, and shows up as water use rather than noise you can hear from another room.
What you can do yourself before ordering a part
Before buying anything, check whether the flapper has simply shifted out of position or has debris caught under it, such as limescale grit or a bit of grit from the mains. Lifting it, wiping the seat clean, and setting it back down sometimes solves the problem for nothing.
For the fill valve, check that the float arm isn't catching on the side of the tank or the fill valve body, and that the float itself hasn't cracked and filled with water, which stops it rising properly. A cracked float needs replacing rather than adjusting.
Both parts are inexpensive and sold in any hardware shop in Tallinn, and fitting either is usually straightforward if the water shut-off valve under the cistern still works. If that valve is seized, which is common in older buildings, you may not be able to isolate the water yourself.
- Take the lid off and check the water level against the overflow tube
- Lift the float by hand to see whether the water stops
- Add food colouring to the tank and check the bowl after ten minutes
- Wipe debris off the flapper seat and check it seats flat
- Check the float for cracks and the arm for obstructions
- Confirm the shut-off valve under the cistern actually turns
Why constant running costs more than it looks like
A toilet that runs continuously, or restarts every few minutes, can use a genuinely large amount of water over a month, and in Estonia water and sewage are billed together, so the cost is doubled on the bill compared with what the tap alone would suggest.
Because the sound fades into the background after a day or two, many households don't notice how long it's been running for. It's worth checking the water meter reading against a previous bill if you suspect the toilet has been running for a while.
The parts themselves cost very little next to what weeks of continuous running add up to, which is really the main reason to deal with it promptly rather than getting used to the noise.
When to call someone instead of trying it yourself
If the shut-off valve under the cistern won't turn, if the cistern is an older or unusual model where parts don't match what's sold locally, or if you've replaced the flapper or the fill valve and the problem hasn't gone away, it's worth calling someone rather than guessing further.
Our toilet repair and fitting work starts from 60 € per job and covers exactly this kind of diagnosis and part replacement, done once rather than in stages. For a running toilet tangled up with other plumbing, such as a stiff shut-off valve or a pipe that needs attention too, plumbing work is billed from 45 € an hour.
If it turns out to be a small, one-off fix that doesn't need a plumber specifically, our odd jobs service from 39 € an hour covers that too. We work in Tallinn and Harju county and can usually get to a running toilet quickly, since it's not a job that improves with waiting.
Lift the float and check the flapper first: a running toilet is nearly always one of these two cheap parts, but the water bill keeps rising until it's fixed.