That faint hiss or the tank refilling every few minutes is more than an annoyance. A running toilet can waste 200 to 750 litres of water a day, and on a metered water bill in Ontario that adds up to hundreds of dollars a year. The fix is almost always one of four cheap parts inside the tank, and none of them need a plumber. This guide shows you how to diagnose the cause in three minutes and repair it in under an hour.
Key takeaways
- Most running toilets are caused by a worn flapper ($8–$20), a float set too high (free) or a failed fill valve ($15–$35).
- The food-colouring test tells you in 15 minutes whether the flapper is leaking.
- Water level should sit about 2.5 cm (1") below the top of the overflow tube. Higher than that and the tank drains into the overflow forever.
- Replacing a fill valve takes 30 minutes with an adjustable wrench and a towel.
- If the toilet is over 20 years old, uses 13 L per flush and needs a third repair, replacing it with a dual-flush model saves more water than any fix.
How a toilet tank works (60-second version)
Lift the lid and you will see four parts:
- Fill valve (left side, tall tower or older ballcock): refills the tank after a flush and shuts off when the float rises.
- Float: a cup around the fill valve, or a ball on an arm. It tells the fill valve when the tank is full.
- Flush valve and flapper (centre): the rubber flap lifts when you push the handle and lets water rush into the bowl, then drops to seal the tank.
- Overflow tube: the open pipe next to the flapper. If water rises above the top, it drains into the bowl so the tank cannot overflow.
A toilet "runs" when water keeps leaving the tank (leaking past the flapper or over the overflow tube) and the fill valve keeps replacing it.
Diagnose it in three minutes
| What you notice | Likely cause | Go to |
|---|---|---|
| Water trickling into the overflow tube constantly | Float set too high, or fill valve not shutting off | Fix 2, then Fix 4 |
| Tank refills for a few seconds every 5–30 minutes ("phantom flush") | Flapper leaking | Fix 1 |
| Runs continuously right after a flush, stops if you jiggle the handle | Chain too short or tangled, flapper held open | Fix 3 |
| Hissing sound, water level correct | Fill valve seal worn, or debris in the valve | Fix 4 |
| Weak flush and the tank never fills fully | Float set too low, or a clogged fill valve | Fix 2, then Fix 4 |
The food-colouring test
- Remove the tank lid and add 10 drops of food colouring (or a dye tablet from the hardware store) to the tank water. Do not flush.
- Wait 15–20 minutes.
- Look in the bowl. If the water is tinted, the flapper is leaking. If it is clear, the flapper is fine and the problem is the fill valve or float.
Fix 1: Replace the flapper
Flappers are rubber, and rubber hardens, warps and grows mineral deposits. In-tank bleach tablets destroy them in a year or two. Replacement takes ten minutes.
- Close the shut-off valve behind the toilet (clockwise) and flush to empty the tank. Sponge out the last inch of water.
- Unclip the chain from the flush handle lever.
- Unhook the flapper from the two pegs on the sides of the overflow tube (or slide the ring off the tube on some designs).
- Take the old flapper to the store. Flappers come in 2" (most toilets before 2005 and many budget toilets) and 3" (most modern high-efficiency toilets). Match the size and, if possible, the brand; a "universal" flapper often does not seal perfectly on a toilet designed for a specific one.
- Wipe the flush valve seat with a cloth so the new flapper seals on a smooth surface. If the seat is rough or pitted, a flush valve seat repair kit ($10) fixes it without removing the tank.
- Install the new flapper, reconnect the chain with about 1 cm of slack, open the water and test-flush three times.
Fix 2: Adjust the float and water level
Look at the water level with the tank full. It should be about 2.5 cm (1") below the top of the overflow tube, and many tanks have a fill line moulded on the back wall. If water is at or above the top of the tube, it is draining into the bowl continuously.
- Cup float on a tower fill valve (most toilets since 2000): pinch the metal clip on the rod beside the float and slide the cup down to lower the level, or turn the adjustment screw on top of the valve counter-clockwise.
- Ball float on a brass arm (older toilets): gently bend the arm downward to lower the level, or turn the screw at the pivot. If the ball has water inside it, replace it.
- Flush and check the new level. Adjust again if needed.
Fix 3: Adjust the chain and handle
- The chain should have about 1 cm of slack when the flapper is closed. Too tight and the flapper cannot seal; too loose and it does not lift fully, causing a weak flush and the chain can catch under the flapper.
- Move the clip to a different link, or trim excess chain so it cannot tangle.
- If the handle sticks in the down position, loosen the nut inside the tank (it is reverse-threaded on many toilets: turn clockwise to loosen) and clean the lever, or replace the handle assembly ($10–$20).
Fix 4: Replace the fill valve
If the water level is right and the flapper passes the dye test but the toilet still hisses or refills, the fill valve is not shutting off. Sometimes debris is the cause: lift the cap on top of the valve, hold a cup over it and open the water briefly to flush grit out. If that does not fix it, replace the valve. A universal fill valve costs $15–$35 and fits almost every toilet.
- Close the shut-off valve, flush, and sponge the tank dry. Put a towel and a small bucket on the floor under the tank.
- Disconnect the supply line from the bottom of the fill valve (the nut under the tank on the left).
- Unscrew the large plastic lock nut under the tank that holds the fill valve, and lift the old valve out.
- Adjust the new valve's height so the top of the valve is about 2.5 cm above the top of the overflow tube (twist the body to lengthen or shorten it; there is usually a critical-level mark to line up).
- Set the valve into the hole with its rubber washer inside the tank, and tighten the lock nut from below by hand plus a quarter turn with pliers. Do not overtighten; the porcelain can crack.
- Clip the refill tube onto the overflow tube so it discharges into the tube, not into the tank. This small tube refills the bowl; if it sits below the water line it will siphon.
- Reconnect the supply line, open the water slowly and check under the tank for drips.
- Set the float for the correct water level, then flush a few times.
Still running? Check these
- Cracked overflow tube. Water leaks through a hairline crack below the water line. The whole flush valve must be replaced, which means removing the tank (1–2 hours, $20–$40 in parts).
- Refill tube pushed too far into the overflow. If it reaches below the water level in the tube it can siphon the tank. Clip it at the top of the tube.
- Water pressure over 80 psi. Fill valves cannot seal against very high pressure. A pressure-reducing valve on the main is the fix.
- Warped flush valve seat on old plastic flush valves. A new flapper will never seal. Replace the flush valve.
What a running toilet actually costs
| Leak | Water wasted per day | Extra cost per year (approx., at $4/m³ water + sewer) |
|---|---|---|
| Slow flapper leak (phantom flush every 30 min) | 100–200 L | $150–$300 |
| Constant trickle into overflow | 300–750 L | $450–$1,100 |
| Flapper stuck open | 1,000+ L | $1,500+ |
Compare that with $8 for a flapper or $25 for a fill valve, and there is no reason to put the repair off another week.
When to replace the toilet instead
If your toilet was installed before 1995, it probably uses 13 L (3.5 gallons) or more per flush. Even after you fix the leak, it uses two to three times the water of a modern 4.8 L or dual-flush toilet. Municipalities across Ontario have offered rebates for replacing them for exactly that reason. A new dual-flush toilet typically pays for itself in water savings within a few years for a family of four, and it comes with a fresh flapper, fill valve and a fully glazed trapway that clogs less.
Ready for a toilet that just works?
Dual-flush, one-piece and wall-hung toilets from MyBath, Toto and Duravit. Delivered across Ontario, free on orders over $600.
Frequently asked questions
Why does my toilet run every few minutes?
Water is slowly leaking past the flapper into the bowl. When the tank level drops enough, the fill valve tops it up for a few seconds. Do the food-colouring test to confirm, then replace the flapper.
How do I stop a toilet from running without a plumber?
Lift the lid and check three things: the water level (should be 2.5 cm below the overflow tube), the flapper (replace if warped or leaking) and the chain (1 cm slack). Those three steps fix about 90% of running toilets.
How much does it cost to fix a running toilet?
DIY: $8–$35 in parts. A plumber in Ontario charges $120–$250 for the same repair. A new flush valve (tank removal) runs $200–$350 installed.
Can a running toilet increase my water bill?
Significantly. A moderate leak wastes 300 litres a day, which is over 100,000 litres a year. Many homeowners discover the leak only when the municipality flags unusual consumption.
How do I know if I need a 2-inch or 3-inch flapper?
Measure the opening of the flush valve at the bottom of the tank. If it is about the size of a baseball, it is 2". If it is closer to a softball, it is 3". Most toilets made after 2005 use 3".
Should I repair or replace an old toilet?
If it is a 13 L pre-1995 toilet, replace it. The water savings from a modern dual-flush toilet outweigh the cost of repeated repairs, and the new toilet flushes better.
