Running Toilet Diagnosis and Repair

Purpose

This procedure names which of two seats is leaking before anybody buys a part. A toilet that runs is water crossing one of exactly two seals: the flush valve seal at the bottom of the tank, letting tank water into the bowl, or the fill valve at the top, letting supply in faster than it shuts off. A tech who guesses is right about half the time, and the wrong half is a return trip. EPA WaterSense puts a running toilet at up to 200 gallons a day, so the customer arrives already annoyed about a bill, which makes a diagnosis you can show them worth more than a fast part swap.

Scope

Covers diagnosis and in-tank repair of a running or intermittently refilling tank-type water closet, residential and light commercial: level and dye testing, seal and seat assessment, fill valve isolation, and the verification that closes the call.

Does not cover replacing the flush valve body or tank-to-bowl hardware, which means pulling the tank and belongs to the toilet rebuild and internal replacement SOP; a leak at the base, which the toilet replacement standard owns; a flushometer bowl, which has no tank; or a bowl that will not clear, which goes to the drain cleaning standard.

Roles and the handoff

Procedure

1. Get the sound pattern before you touch anything. A continuous hiss, a burst of refill with nobody using the fixture, or a run that follows a flush. Acceptance: one of the three on the ticket, with an interval in minutes for the burst pattern. Wrong: "it just runs", which fits all three. Stop rule: do not open a part off a pattern nobody has named; continuous points at the fill valve, bursts at the seal, post-flush running at chain or float. Hazard: check the floor before you kneel, since a running fixture has been mopped around and wet tile is the most common residential slip.

2. Take the lid off and put it where it cannot fall. Lift straight up with both hands onto a folded towel outside the traffic path. Acceptance: lid flat, off the fixture, leaning on nothing. Wrong: lid on a vanity edge or on end against a wall. Stop rule: a chipped lid is customer property damaged and goes on the damage record immediately. Hazard: a vitreous china lid commonly runs 8 to 12 lb and breaks into edged pieces, so two hands, never one-handed past a person.

3. Read the static level against two references: the moulded fill line and the top of the overflow tube. Acceptance: the level sits on the moulded line, about 1 in below the tube top on most tanks, nothing curling over the lip. Wrong: a level at or above the tube top with a sheet running down it. Stop rule: a level above the tube is a fill valve or float fault, and a valve overfilling into the overflow imitates a failed flapper exactly, so steps 6 and 7 wait until step 8 clears it. Hazard: with an in-tank cleaner tablet present the tank water is dilute bleach or acid, so gloves on before your hand goes in, nothing splashed at your face, and tell the customer the tablet destroyed the old seal and will take the new one.

4. Dye test the flush valve seal. Dye in, stir once, fixture unused for 10 to 15 minutes. Acceptance: no colour in the bowl at 15 minutes. Wrong: colour inside that window. Stop rule: dye in the bowl puts the fault at the flush valve seal and sends you to step 6; a clean bowl on an audibly running fixture sends you to step 8; if somebody flushed it, re-run rather than reason from a spoiled test. Hazard: none; the discipline is keeping the household off the fixture for the window.

5. Close the stop and mark the level to confirm direction of travel. Close the stop, tape a mark at the water line, wait 15 minutes. Acceptance: with supply isolated, the level holds at the mark. Wrong: it falls away from the mark. Stop rule: a falling level with supply closed proves water is leaving downward and confirms step 4; a level that holds while the fixture still runs puts the fault at the fill valve. Hazard: closing an old multi-turn stop is where a corroded stem shears or a chrome nipple splits, so back the body up with a second wrench, stage a pan and towels first, and never force one that has seized.

6. Identify the flush valve seal by measurement, not memory. Flush the tank empty and measure across the seat. Acceptance: about 2 in or about 3 in, seal recorded as a hinged flapper, a canister seal on a tower, or an integral tower seal. Wrong: assuming a 2 in flapper because that is what is on the truck. Stop rule: a 3 in valve fitted with a 2 in conversion leaks immediately, so if the matching seal is not stocked, quote the return trip with the part rather than improvising. Hazard: the tank floor carries bolt heads and a corroded refill clip, so the gloves from step 3 stay on.

7. Inspect the seat, not just the seal. Drag a gloved fingertip round the full seat circumference, and check the seal for cupping, hardening and chain condition. Acceptance: seat continuous and smooth, no ridge, no pitting; seal pliable rather than stiff; chain carrying about 1/2 in of slack with the flapper down. Wrong: a ridge you can feel, a seal gone hard, or a chain tight enough to hold the flapper cracked open. Stop rule: a mineral ridge on a brass seat gets dressed with a seat pad and re-checked; a cut or deformed plastic seat cannot be dressed, which is a flush valve replacement under the rebuild SOP, quoted before anything else comes apart. Hazard: dressing a seat throws scale grit up at eye height while you lean over the tank, so eye protection before the pad touches it.

8. Test the fill valve for its two faults: where the refill tube discharges, and whether the valve shuts off. Acceptance: the refill tube discharges ABOVE the overflow opening rather than inside it, the valve shuts off cleanly with the level on the moulded mark, and its critical level mark sits at least 1 in above that opening, as ASSE 1002 requires and IPC Section 425 or UPC Chapter 4 adopts in the edition your jurisdiction enforces. Wrong: a refill tube pushed into the overflow, which siphons the tank down and imitates a leaking flapper, or a valve that hunts and never closes. Stop rule: a valve that will not shut off cleanly once the level is right gets replaced, not adjusted again; a critical level below that 1 in is a backflow defect replaced whether or not it caused the complaint. Hazard: none; keep your sleeve out of the tank so you do not move the float you are reading.

9. Replace only the part the tests named, and set the level to the mark. Fit the matching seal or valve, set the float so the level lands on the moulded line, chain slack about 1/2 in. Acceptance: the part matches what step 6 or step 8 recorded, and the level rests on the line rather than near it. Wrong: replacing both seats because it feels thorough, which makes a repeat failure unattributable to either. Stop rule: if fitting the new part shows the other seat was the fault, stop and re-run step 4 rather than adding parts. Hazard: the old parts are the sharp end, carrying scale edges, and the shank nut will crack the tank if torqued, so hand-tight plus a light snug and no wrench past that.

10. Re-pressurize slowly and re-verify the protection you disturbed. Open the stop with a hand on the valve and let the tank fill through a full cycle. Acceptance: all five close-out checks pass - valve shutting off with the level on the moulded line, refill tube above the overflow opening, critical level at least 1 in above it, a fresh 15-minute dye test clean, and three consecutive flushes clearing without hunting. Wrong: any of the five, particularly a refill tube pushed into the overflow during the work. Stop rule: dye in the bowl on the close-out means the repair failed, so go back to step 7 and read the seat again rather than fitting a second seal to it. Hazard: first pressurization is when a stop that survived being closed lets go, at the height of a kneeling tech's face, so open a quarter turn at a time with a pan under the stop and eyes on the packing nut.

The record this produces

Six fields, written before the tech leaves: the sound pattern from step 1, the static level relative to the moulded mark in inches, the dye result and minutes to first colour, the flush valve size and seal type from step 6, the seat condition from step 7, and the fill valve verdict from step 8. Photograph the seat and the fill valve head.

They land against the fixture, not just the customer. The tech on a repeat call reads seat condition first and knows in ten seconds whether the last visit fitted a seal to a bad seat; the office reads dye result and part fitted to decide whether a second call the same season is warranty.

One worked pass, including a failure

Powder room, mid-1990s house, complaint is that the toilet refills by itself at night.

Step 1: a refill burst three or four times an hour with nobody using it, the intermittent-burst pattern. Step 2 clean. Step 3: static level 3/4 in below the overflow tube top against a moulded mark 1 in below it, so the level is 1/4 in high. A finding, not a stop, recorded because a high level makes a marginal seal leak sooner.

Step 4 fails as the pattern predicts: dye in the bowl at 6 minutes, inside the 15-minute window.

Step 5 confirms direction independently. Stop closed, level marked, and at 15 minutes the level has fallen 1-1/8 in, which is 4-1/2 in per hour. A fill valve triggering on roughly 1 in of drop fires about four times an hour, matching what the household reported.

Step 6: the opening measures 3 in, canister seal lifting on a tower, matching seal on the truck.

Step 7 FAILS and takes its stop rule. The fingertip drag finds a raised, gritty ridge about a third of the way round, and under a light it is not scale on brass, it is a moulded plastic seat cut across the sealing face. That cannot be dressed, so it becomes a flush valve replacement: pulling the tank, and outside this SOP. The tech photographs the seat, quotes the flush valve and tank-to-bowl kit, and the lead approves before anything else is loosened.

Step 8 still runs, because the 1/4 in high level is unexplained. Refill tube clipped above the overflow opening, critical level 1-1/4 in above it, valve shutting off cleanly once the float is reset. The fill valve is sound; the high level was an earlier repair's adjustment, recorded so the next tech does not chase it.

Steps 9 and 10 close the job after the rebuild work: level on the moulded mark, refill tube above the overflow opening, critical level 1-1/4 in above it, dye test clean at 15 minutes, three consecutive flushes clearing without hunting.

When the site does not match this procedure

Customer wants both seats replaced regardless of the tests: their fixture, so do it, but record which part the tests implicated, or a repeat leak has two suspects and no evidence.

Fixture discontinued, no matching seal: do not fit a conversion kit to a valve never designed for one. Price the flush valve and the fixture, and let the customer choose against the toilet's age.

Tank dry and bowl water moving: not this procedure. A lost trap seal is a venting or siphon question, and it goes to the annual plumbing inspection SOP.

References

• ASSE 1002, the anti-siphon fill valve standard behind the critical level check in steps 8 and 10.
• IPC Section 425 or UPC Chapter 4, in the edition your authority having jurisdiction has adopted, which is how that requirement reaches you through the inspection.
• EPA WaterSense material on household leaks, for the daily loss figure quoted in the opener.
• Fixture and valve manufacturer instructions for flush valve size, seal part number and the tank water line.
• See related: the Plumbing toilet rebuild and internal replacement SOP, which owns any repair needing the tank off, and the Plumbing toilet replacement standard, which owns leaks at the base.