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Safety Cue
Task-specific safety guidance for ordinary work hazards.
Project 12
Repair a Running Toilet and Replace Tank Parts
Diagnose the exact cause of a running toilet using observation and a dye test, then correct it with compatible replacement tank components — flapper, fill valve, or flush valve — and verify the repair with a marked water level, repeated flush cycles, and a second dye test.
Field Cue System
These cues appear at the point of work. They identify safety, code, manufacturer, and measurement issues before they become water damage, a failed repair, or a repeat service call.
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Critical Safety Cue
Serious injury, water damage, or a stop-work condition is possible.
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Field Safety Cue
Practical work-area safety: footing, cabinet protection, and housekeeping.
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Code Alert
Local requirements vary. Verify fixture and fill-valve fill-level rules.
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Manufacturer Cue
Follow product-specific instructions for the exact flapper, fill valve, and flush valve installed.
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Measurement Cue
Reference-point, water-level, and verification guidance.
Job Overview
This project qualifies you to diagnose and correct a running toilet using compatible replacement tank components and measured operational checks. The finished work product is a toilet tank that fills to the correct, marked water level, shuts off reliably, holds water without leaking into the bowl, and flushes normally through repeated test cycles.
You will observe the symptom without disturbing any part first, mark the current water level, run a dye test to confirm whether water is leaking past the flapper into the bowl, inspect every tank component that can cause running water, classify the verified cause, replace only the component or components the diagnosis supports, and confirm the repair with a second dye test and multiple flush cycles.
This project builds directly on the toilet-setting skills from Chapter 11 and reuses the shutoff and drain-down discipline from Chapter 1. It prepares you for Chapter 13, where the same diagnose-before-you-disassemble approach applies to a shower valve cartridge.
Skills You Will Demonstrate
- PL-067 — Diagnose the verified cause of a running toilet using observation, a marked water level, and a dye test.
- PL-068 — Replace the fill valve when diagnosis confirms fill-valve failure.
- PL-069 — Replace the flush valve when diagnosis confirms a flush-valve-body defect.
- PL-070 — Replace the flapper when diagnosis confirms a compatible flapper leak.
- PL-071 — Adjust the water level to the marked or manufacturer-specified setting.
- PL-072 — Verify proper operation through a repeated dye test and multiple flush cycles.
Where This Skill Fits
A running toilet is one of the most common residential plumbing service calls, and it is also one of the most frequently misdiagnosed. Replacing a fill valve when the actual cause is a leaking flapper wastes the cost of the part and does not fix the symptom; replacing a flapper when the flush-valve seat itself is damaged produces the same result. This project trains the evidence-first sequence — observe, mark, dye-test, inspect, classify — before any part is removed.
The tank-removal and reassembly steps used when a flush valve requires replacement reuse the tank-to-bowl hardware handling taught in Chapter 11. The shutoff and drain-down discipline from Chapter 1 controls how the tank is isolated before any component is disturbed.
Scope and Intended Use
This project covers:
- observing the running-toilet symptom and marking the current tank water level before disturbing any part
- running a dye test to confirm or rule out water leaking into the bowl without flushing
- inspecting the fill valve, float, refill tube, flapper, chain, flush-valve seat, handle, and overflow tube
- classifying the verified cause as overfill, leaking flapper, damaged flush-valve seal, chain interference, refill-tube siphoning, fill-valve failure, or another verified condition
- replacing the flapper, the fill valve, or the flush valve — individually or in combination — based on the diagnosed cause
- adjusting the tank water level to the marked or manufacturer-specified setting
- verifying the repair with a repeated dye test and multiple flush cycles
This project does not authorize the learner to:
- replace a component that the dye test and inspection have not confirmed as the cause
- set the toilet on a new closet flange, replace the wax ring or seal, or perform any work covered by Chapter 11
- correct a cracked tank, a cracked bowl, a broken closet flange, or a structurally unstable toilet — these are stop-work conditions requiring the Chapter 11 replacement sequence or a qualified professional
- proceed with reassembly when a stop-work condition identified in this chapter is present and uncorrected
Any component, tank condition, or fixture defect that fails verification in this chapter must be corrected, repaired, or escalated to a qualified professional before the toilet is returned to service.
Reference Conventions
Establish these references before any component is disturbed, and do not change the defined diagnosis mid-project.
| Term | Definition |
|---|---|
| Marked water level | The current tank water line marked directly on the tank wall before any component is disturbed |
| Critical level | The fill-valve manufacturer's minimum air-gap relationship between the water level and the overflow-tube opening, used to prevent backflow into the fill valve |
| Verified cause | The specific condition — overfill, leaking flapper, damaged flush-valve seal, chain interference, refill-tube siphoning, fill-valve failure, or another confirmed condition — identified through the dye test and component inspection |
| Dye test | Adding approved dye to the tank and checking the bowl for color without flushing, used to confirm or rule out a flapper or seat leak |
| Flush-valve seat | The molded opening at the base of the tank that the flapper seals against |
| Stop-work condition | Any observed hazard, fixture defect, or component failure that must halt the project until corrected or escalated, defined in this chapter's failure-point section |
Diagnostic Record
Before disconnecting any tank component, record the observed symptom and diagnostic findings directly on the Running-Toilet Repair Worksheet:
Toilet location: ______ Model / manufacturer (if visible): ______ Observed symptom: ______
Marked water level correct: ______ (Yes/No) Dye test result: ______ (Dye entered bowl / No dye in bowl) Verified cause: ______
Prerequisites
- Completion of Chapter 1 (shutoff, drain-down, and work-area protection) and Chapter 11 (toilet setting and tank-to-bowl hardware) or equivalent competency
- Access to the toilet's fixture stop and confirmation that it operates and fully closes
- Manufacturer service information for the toilet model, when available, including specified water level and compatible replacement parts
- Basic hand tools and PPE listed in the Tools, Equipment, Materials, Consumables, and PPE tables above
- A stop-work decision authority — the learner, supervisor, or licensed professional who will be notified if a stop-work condition is found
Common Field Fundamentals
Every running-toilet repair follows the same four-part sequence: observe, confirm, classify, correct. Skipping the confirmation step and jumping straight to a part replacement is the single most common cause of a repeat service call for this symptom.
ObserveSymptom noted without removing any part first
MarkCurrent water level marked on the tank wall
Dye testApproved dye added; bowl checked without flushing
InspectFill valve, float, refill tube, flapper, chain, seat, handle, and overflow tube checked
ClassifyCause identified from confirmed evidence, not assumption
CorrectOnly the confirmed component replaced or adjusted
Reset levelWater level returned to the marked or specified setting
VerifyDye test repeated and multiple flush cycles observed
Distinguishing the Common Causes
An overfill condition sends water continuously into the overflow tube and is confirmed by comparing the marked water level to the overflow-tube opening. A leaking flapper or damaged flush-valve seat allows water to pass from the tank into the bowl without flushing, and is confirmed by the dye test. Chain interference prevents the flapper from seating fully and is confirmed by observing the chain length and flapper closure directly. A siphoning refill tube is confirmed by observing the tube positioned below the overflow-tube water level. A failing fill valve is confirmed when it will not shut off, cannot be adjusted to stop at the correct level, leaks internally, or is incompatible with the tank.
PL-067 – PL-072
Diagnostic / Tank-Component Replacement Qualification
Repair a Running Toilet and Replace Tank Parts
A. Finished-Project Specification
Quantity: one toilet tank diagnosed, one verified cause classified, one or more compatible tank components replaced or adjusted to match the diagnosis, and one completed Running-Toilet Repair Worksheet documenting the cause, the correction, and the verification result.
B. Component Schedule
| Component | Quantity | Material | Finished Condition | Preparation |
|---|---|---|---|---|
| Flapper | 1 (if diagnosis confirms) | Manufacturer-compatible rubber or synthetic seal | Seats fully on the flush-valve seat with no visible gap | Matched to seat size and model before installation |
| Fill valve | 1 (if diagnosis confirms) | Manufacturer-compatible fill-valve assembly | Shuts off completely at the correct water level | Shank seal and locknut installed without overtightening |
| Flush valve | 1 (if diagnosis confirms) | Manufacturer-compatible flush-valve body, gasket, and locknut | Installed in the specified orientation with a leak-free tank-to-bowl seal | Tank removed and reinstalled per Chapter 11 hardware sequence |
| Refill tube and clip | 1 set (if repositioned) | Manufacturer-supplied tubing and clip | Positioned above the overflow-tube water level | Routed without insertion below the critical level |
C. Diagnostic and Verification Schedule
| Item | Target Condition | Verification Method |
|---|---|---|
| Marked water level | Marked on the tank wall before any component is disturbed | Visual confirmation before disassembly |
| Dye test (first) | Confirms or rules out a flapper or flush-valve seat leak | Dye observed in bowl or absence confirmed without flushing |
| Component inspection | Fill valve, float, refill tube, flapper, chain, seat, handle, and overflow tube checked individually | Direct visual and operational inspection |
| Verified cause | Classified from confirmed evidence before any part is replaced | Written classification on worksheet |
| Water-level reset | Returned to the marked or manufacturer-specified setting | Direct comparison to the tank-wall mark |
| Dye test (second) | No dye enters the bowl after the repair | Repeated dye test after restoring water |
| Flush cycles | Refill, shutoff, flapper seating, handle operation, and bowl refill confirmed across multiple cycles | Direct observation of repeated operation |
D. Fastener and Hardware Schedule
| Joint | Fastener / Hardware | Installation Notes |
|---|---|---|
| Fill-valve shank to tank | Fill-valve locknut and shank seal supplied with the fill valve | Hand-tighten, then apply only the manufacturer's specified additional turn; do not overtighten against the tank |
| Flush-valve body to tank | Flush-valve locknut and tank-side gasket supplied with the flush valve | Tighten evenly while supporting the flush-valve body to keep it square in the tank opening |
| Tank to bowl (when tank is removed) | Tank-to-bowl bolts, washers, and nuts per Chapter 11 hardware sequence | Tighten alternately and evenly only enough to compress the tank-to-bowl gasket without cracking the tank |
| Refill-tube clip | Manufacturer-supplied clip | Positioned so the tube outlet remains above the overflow-tube water level |
E. Acceptance Standards
| Check | Standard |
|---|---|
| Diagnosis | Verified cause confirmed by dye test and direct component inspection before any part is replaced |
| Water level | Matches the marked or manufacturer-specified setting and maintains the required critical-level relationship to the overflow tube |
| Flapper seal | Seats fully on the flush-valve seat with no dye passing into the bowl during the repeated dye test |
| Fill-valve shutoff | Shuts off completely at the correct level across repeated flush cycles with no continuous trickle |
| Flush-valve seal (if replaced) | Tank-to-bowl connection is leak-free under static and flushing conditions |
| Handle and chain | Handle returns freely, chain has enough slack for full flapper closure without excessive delay |
| Documentation | Running-Toilet Repair Worksheet complete with symptom, dye-test results, verified cause, replaced components, and final results |
F. Observation and Baseline Documentation
- Identify the toilet model, tank components, specified water level, flush-valve size, flapper type, and manufacturer service information. Record what is visible on the tank or lid before removing anything.
- Observe the symptom without removing parts. Note whether the running is continuous, intermittent, or triggered only after a flush.
- Mark the current tank water level and inspect whether water enters the overflow tube. Use a permanent marker directly on the tank wall.
G. Dye Test and Component Inspection
- Add approved dye to the tank and check for leakage into the bowl without flushing. Wait several minutes and observe the bowl water for color before touching any component.
- Inspect the fill valve, float, refill tube, flapper, chain, flush-valve seat, handle, and overflow tube. Check each component individually and record its condition.
- Classify the cause as overfill, leaking flapper, damaged flush-valve seal, chain interference, refill-tube siphoning, fill-valve failure, or another verified condition. Base the classification on the dye-test result and the component inspection, not on assumption.
H. Isolation and Component Replacement
- Shut off and drain the tank. Use the Chapter 1 isolation and drain-down sequence at the toilet's fixture stop.
- Replace the flapper first when testing confirms a compatible flapper leak and no flush-valve-body defect exists. Match the replacement to the seat size and model.
- Set chain slack to permit full closure without excessive delay. Adjust the chain length so the flapper seats fully after each flush.
- Replace the fill valve when it does not shut off, cannot adjust correctly, leaks, or is incompatible. Select a compatible replacement before beginning removal.
- Install the fill-valve shank seal and locknut without overtightening. Hand-tighten, then apply only the manufacturer's specified additional turn.
- Set valve height and critical-level relationship according to the manufacturer and code. Confirm the relationship to the overflow-tube opening before restoring water.
- Route the refill tube using the approved clip without inserting it below the overflow water level. Confirm the tube outlet position after clipping.
I. Flush-Valve Replacement (When Confirmed)
- Remove the tank when replacement of the flush-valve body is required. Use the Chapter 11 tank-removal and support sequence.
- Replace tank-to-bowl seals and hardware when disturbed. Do not reuse a compressed or damaged tank-to-bowl gasket.
- Install the compatible flush valve, gasket, and locknut in the specified orientation. Confirm orientation before tightening the locknut.
- Reassemble the tank evenly and reconnect the supply. Tighten tank-to-bowl hardware alternately and evenly.
J. Restoration and Verification
- Restore water and adjust the tank level to the marked or manufacturer-specified setting. Compare directly to the tank-wall mark made in Step F.3.
- Perform the dye test again. Confirm no dye passes into the bowl without flushing.
- Operate multiple flush cycles and verify refill, shutoff, flapper seating, handle operation, and bowl refill. Observe at least three complete cycles.
- Inspect all disturbed seals and fasteners for leakage. Check the fill-valve shank, flush-valve locknut, tank-to-bowl connection, and supply connector.
- Document the diagnosed cause, replaced components, adjustments, and final results. Complete every field on the Running-Toilet Repair Worksheet.
Common Readiness Inspection
Inspect every completed repair using the same checks regardless of which component was replaced.
- Diagnosis check: confirm the verified cause was classified from dye-test and inspection evidence, not assumed.
- Level check: confirm the water level matches the marked or specified setting and the critical-level relationship to the overflow tube.
- Dye-test check: confirm no dye passes into the bowl after the repair.
- Cycle check: confirm refill, shutoff, flapper seating, handle operation, and bowl refill across at least three flush cycles.
- Seal check: confirm every disturbed seal and fastener is leak-free under static and flushing conditions.
- Documentation check: confirm the Running-Toilet Repair Worksheet is fully completed.
Complete the Running-Toilet Repair Worksheet in the Inspection Checklist section below before returning the toilet to service.
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Failure Points and Troubleshooting
Cleanup
This project ends with the toilet returned to normal service, tested, and documented.
- Dispose of old flapper, fill-valve, or flush-valve components according to local waste requirements
- Wipe down the tank exterior and surrounding floor of any spilled tank water or dye residue
- Confirm the fixture stop remains fully open and accessible
- Store any unused compatible replacement parts with their manufacturer packaging for future reference
- File the completed Running-Toilet Repair Worksheet with the fixture's service record
Field Terms
- Marked Water Level
- The current tank water line marked directly on the tank wall before any component is disturbed.
- Critical Level
- The fill-valve manufacturer's minimum air-gap relationship between the water level and the overflow-tube opening, used to prevent backflow into the fill valve.
- Verified Cause
- The specific condition identified through the dye test and component inspection that explains the running-toilet symptom.
- Dye Test
- Adding approved dye to the tank and checking the bowl for color without flushing, used to confirm or rule out a flapper or seat leak.
- Flush-Valve Seat
- The molded opening at the base of the tank that the flapper seals against.
- Refill Tube
- The small tube that directs a portion of incoming fill water into the overflow tube to refill the bowl trap after a flush.
- Chain Slack
- The amount of free chain length between the flush handle arm and the flapper, set to allow full flapper closure without excessive delay.
- Running-Toilet Repair Worksheet
- The document recording the observed symptom, dye-test results, verified cause, replaced components, adjustments, and final verification results.
Skill Check
- Why must the water level be marked and a dye test run before any tank component is removed?
- What does a positive dye test confirm, and what does it rule out?
- What conditions indicate that the fill valve, rather than the flapper, is the verified cause of a running toilet?
- Why must chain slack be set precisely rather than left with excess length?
- What is the critical-level relationship, and why does code control it rather than personal preference?
- When is tank removal required for this project, and which chapter's hardware sequence controls that step?
- How does the learner confirm that a repair has actually corrected the symptom rather than only appearing to?
- What must the learner do if a replaced component does not resolve the running-toilet symptom?
- Why must a compatible, model-matched flapper or fill valve be used instead of any similarly sized universal part?
- What information must be recorded on the Running-Toilet Repair Worksheet before the toilet is returned to service?
Competency Rubric
| Competency | Independent Pass Standard | Not Demonstrated | With Assistance | Independently |
|---|---|---|---|---|
| PL-067 | Diagnoses the verified cause of a running toilet using observation, a marked water level, and a dye test before any component is replaced | |||
| PL-068 | Replaces the fill valve correctly when diagnosis confirms fill-valve failure, including shank seal, locknut, and critical-level setting | |||
| PL-069 | Replaces the flush valve correctly when diagnosis confirms a flush-valve-body defect, including tank removal, gasket replacement, and leak-free reassembly | |||
| PL-070 | Replaces the flapper correctly when diagnosis confirms a compatible flapper leak, with correct seat match and chain slack | |||
| PL-071 | Adjusts the water level to the marked or manufacturer-specified setting while maintaining the required critical-level relationship | |||
| PL-072 | Verifies proper operation through a repeated dye test and multiple flush cycles, confirmed by direct observation |
Mark one column per competency. Only Demonstrated Independently awards the competency; Demonstrated with Assistance authorizes additional supervised practice but does not complete the requirement.
Inspection Checklist — Running-Toilet Repair Worksheet
| Item | Target Condition | Result | Pass/Fail | Correction (if any) |
|---|---|---|---|---|
| Observed symptom | Recorded before any part is disturbed | |||
| Marked water level | Marked on tank wall before disassembly | |||
| Dye test (first) | Confirms or rules out flapper/seat leak | |||
| Verified cause | Classified from confirmed evidence | |||
| Component(s) replaced | Matches the verified cause | |||
| Water-level reset | Matches marked or specified setting | |||
| Dye test (second) | No dye in bowl after repair | |||
| Flush cycles | Refill, shutoff, and seating confirmed across 3+ cycles |
Verified cause and correction summary: ____________________________________________
Repair declared complete: ______ (Pass/Fail) Date: ____________ Builder name: ____________
Performance Check
With the diagnosis confirmed, the correct component or components replaced, the water level reset, and the repair verified, review the finished repair against the Acceptance Standards table and confirm the verified cause was classified from dye-test and inspection evidence, the water level matches the marked or specified setting and the critical-level relationship, no dye enters the bowl on the repeated dye test, refill and shutoff are confirmed across at least three flush cycles, and every disturbed seal and fastener remains leak-free. Complete the Running-Toilet Repair Worksheet and correct any failed item before returning the toilet to service. If an item fails, identify whether the error occurred in diagnosis, component selection, installation, level adjustment, or verification before correcting it and re-running the affected check.
Project Closeout
You have completed the twelfth project in the residential plumbing sequence: diagnosing and repairing a running toilet using compatible replacement tank components. This project required you to diagnose running-toilet causes, replace the fill valve, replace the flush valve, replace the flapper, adjust the water level, and verify proper operation (PL-067 through PL-072).
You now have a repeatable diagnose-before-you-disassemble sequence that applies beyond this fixture. That evidence-first approach carries directly into the next project: replacing a shower-valve cartridge and trim using the exact valve manufacturer's procedure.
Retain your Running-Toilet Repair Worksheet as the documented baseline for this fixture. You will use the same observe-confirm-classify-correct sequence for the diagnostic work in Chapter 19.