How to Repair a Leaking Pressure-Assisted Toilet


Pressure-assisted toilets are a popular type of toilet that uses both gravity and compressed air to flush. They are powerful, efficient flushers that can clear waste in just one flush. However, like any toilet, pressure-assisted models can develop leaks over time. A leaking toilet can waste hundreds of gallons of water per day, cause unsanitary conditions, and damage your floors.

In this comprehensive guide, we will cover everything you need to know about repairing a leaking pressure-assisted toilet. We will discuss the common causes of leaks, how to diagnose the problem area, and take you step-by-step through the repair process. With the right information and a few basic tools, you can stop a running toilet and prevent costly water damage and mold growth.

What Is a Pressure-Assisted Toilet and How Does It Work?

Before we discuss repairs, let’s review how a pressure-assisted toilet operates. Unlike a standard gravity flush toilet, pressure-assisted models use air pressure in addition to gravity to siphon water into the bowl.

Here are the key components and functions:

  • Tank – Holds the flush water above the bowl. The tank contains a plastic pressure vessel mounted inside.
  • Pressure vessel – A plastic tank inside the outer ceramic tank. This inner tank uses compressed air to assist flushing.
  • Fill valve – Controls water flow into the tank and pressure vessel after a flush. Shuts off automatically at set tank water level.
  • Flapper – A rubber seal at the tank bottom. Opens to release the flush water from the pressure vessel and outer tank.
  • Flush valve – Opens when the flush lever is pressed, allowing the water to empty from the pressure vessel and outer tank.
  • Air charge unit – Contains a rubber diaphragm or piston inside the pressure vessel. Compresses air to assist flushing.

During a flush, the flush valve opens and the compressed air in the pressure vessel pushes water into the bowl at a high pressure. The air charge assist provides a strong siphon effect to clear the bowl in one flush.

The key benefit of pressure-assist toilets is their powerful, efficient flush. However, the inner pressure vessel and seals create more potential leak points.

Common Causes of Leaks in Pressure-Assisted Toilets

Pressure-assisted toilets can develop leaks just like gravity flow toilets. However, they also have some unique leak points due to their more complex tank design. Here are some of the most common causes of leaks:

  • Damaged or worn flapper – The flapper seal at the bottom of the tank can crack or warp over time, preventing a watertight seal. This allows water to continuously leak from the tank into the bowl.
  • Faulty flush valve seal – The flush valve gasket around the overflow tube may become brittle or misaligned, causing leaks.
  • Cracks in the pressure vessel – If the inner plastic pressure vessel cracks, it can leak water into the outer ceramic tank. Prolonged over-pressurization or dropping something heavy in the tank are common causes.
  • Fill valve failure – If the fill valve fails to shut off properly, the tank and pressure vessel may overfill and leak into the overflow tube. Buildup of sediment or minerals can prevent the fill valve from closing fully.
  • Leaks at tank bolts – The bolts securing the tank to the toilet bowl can loosen over time, causing water to leak at the connections.
  • Damaged lift chain – A corroded or damaged chain connecting the flapper to the flush lever may result in an incomplete flapper closure and leaking.

Diagnosing the Source of the Leak

Pinpointing the exact location of the leak is crucial before attempting repairs. A visual inspection and dye test can help identify the problem area. Here are some tips for diagnosing common pressure-assisted toilet leaks:

Check for water on the floor around the toilet – The first signs of a leak are often visible as water droplets or puddling around the base. Leaks will generally show up around the back of the toilet or underneath near the tank bolts.

Listen for running water – With the tank lid closed, listen closely for sounds of flowing water or dripping. This may indicate continuous flow from the tank through the leak point into the bowl.

Remove the tank lid and look for water movement – With the tank uncovered, check for ripples or obvious water flow. Water leaking into the bowl through a failed flapper will be especially apparent.

Conduct a dye test – Add dye tablets or a few drops of food coloring to the tank water. If colored water appears in the bowl without flushing, this confirms a leak. The dye will help trace the flow pattern to pinpoint the source.

Check for moist areas on tank exterior – Water overflowing from an overfilled tank may leak out onto the tank exterior if the overflow tube is blocked. Watch for drips underneath or moisture on tank sides.

Inspect fittings and seals – Visually examine the flapper, flush valve gasket, tank bolts, fill valve, pressure vessel exterior and other toilet components for cracks, warping, mineral buildup or damage that could cause leaks.

Thoroughly diagnosing the leak before taking any repair steps is important for fixing the problem completely the first time.

How to Repair a Leaking Flapper

The flapper is one of the most prone components to leaking on pressure-assisted toilets. A warped or cracked flapper allows water to continuously drain from the tank into the bowl, resulting in high water bills and potential overflow. Here are tips for replacing a leaking flapper:

Supplies Needed:

  • Replacement flapper seal compatible with your toilet model
  • Adjustable wrench
  • Flat head screwdriver

Steps for Replacing a Faulty Flapper:

  1. Turn off the water supply to the toilet by closing the shutoff valve behind the tank. Flush the toilet to empty the tank.
  2. Use a flat head screwdriver to unscrew the retaining nut holding the flapper chain to the flush lever. Remove the chain from the lever.
  3. Wiggle the flapper free from its mounting hinges in the tank overflow tube. You may need to spread the hinges slightly with a flat head screwdriver to detach the flapper.
  4. Inspect the new replacement flapper and ensure it is the correct size and style for your toilet model. Test fit it on the overflow tube hinges.
  5. Adjust the flapper chain length as needed so there is just enough slack for the flapper to seal fully over the flush valve opening.
  6. Reconnect the flapper chain to the flush lever and secure it with the retaining nut.
  7. Turn on the toilet water supply and allow the tank to fill. Check that the flapper seals completely and water shuts off.
  8. Flush the toilet and observe the flush. If leaking continues, double check the chain/lever connection and flapper seating.

Replacing a faulty, leaking flapper with an new exact fit seal will instantly stop water loss between flushes. Perform regular flapper inspections to identify wear before leaks occur.

Fixing Leaks from the Flush Valve Seal

If the gasket around flush valve at the bottom of the overflow tube is damaged, it can cause water to leak continuously down into the bowl. Reseating or replacing this gasket is straightforward:


  • Thick rubber gasket sized for flush valve (may be included with new flappers)
  • Non-abrasive scrub pad
  • Adjustable wrench


  1. Turn off toilet water supply. Empty the tank.
  2. Remove the old flush valve gasket carefully using fingers. Scrape off any old putty residue.
  3. Scrub the surface of the flush valve clean using a non-abrasive pad. Remove any mineral deposits.
  4. Press the new gasket evenly around the flush valve opening. Ensure it sits flat and makes a tight seal all around.
  5. Tighten the locknut over the gasket using an adjustable wrench. Do not overtighten.
  6. Turn on water supply and let tank refill. Check for any leaks around the new gasket seal.
  7. Readjust or replace the gasket if needed until a tight seal is achieved.

Periodically inspecting and lubricating the flush valve gasket will help prevent drying out and leaks. Catching seal failures early makes simple gasket replacement possible before significant water loss occurs.

How to Repair Leaks from a Damaged Pressure Vessel

If the interior plastic pressure vessel is cracked or damaged, it may leak water down into the outer ceramic tank. Unfortunately, the pressure tank cannot be reliably patched or repaired. Complete replacement is required in most cases of pressure vessel leaks or failure. Here are the steps:


  • Replacement pressure vessel designed for your toilet
  • Adjustable wrench
  • Bucket to catch water
  • Terry rags


  1. Turn off toilet supply valve. Flush to empty tank. Use a rag to soak up any remaining water in the tank.
  2. Disconnect the water supply line from tank fill valve using a wrench. Unbolt tank from bowl.
  3. Lift tank and place onto floor covered with rags. Remove pressure vessel retaining nut or clips.
  4. Maneuver the pressure vessel out through the tank opening. Use a rag to soak up any water spillage.
  5. Inspect new pressure vessel. Ensure it is designed for your toilet make and model. Lubricate the tank gasket with silicone.
  6. Lower the new pressure vessel into the tank. Reattach retaining nut and clips.
  7. Reseal tank to bowl using new rubber washers on tank bolts. Do not overtighten.
  8. Reconnect water supply line to fill valve. Turn on water and allow tank to fill.
  9. Check for any leaks related to the new pressure vessel installation.
  10. Flush the toilet several times to verify proper operation.

Though labor intensive, replacing a irreparably damaged pressure vessel will return your pressure-assisted toilet to like-new performance and prevent leaks.

Fixing a Running Toilet from Fill Valve Issues

Problems with the fill valve are another common source of leaks with pressure-assisted toilets. If the fill valve fails to fully close and stop the water flow at the preset level, the tank and pressure vessel may overfill. This causes water to spill out through the overflow pipe into the bowl, resulting in a constantly running toilet.

Fixing a running toilet just requires servicing or replacing the faulty fill valve:

Supplies Needed:

  • Fill valve repair kit or new fill valve
  • Adjustable wrench
  • Needlenose pliers
  • Terry rag


  1. Shut off the toilet water supply. Flush to empty tank.
  2. Disconnect supply line from fill valve. Unscrew overflow pipe from fill valve.
  3. Remove mounting nut holding fill valve to tank. Lift out fill valve. Place rag in tank to catch drips.
  4. Inspect condition of fill valve. Attempt to clean sediment and mineral buildup with vinegar and scrub brush.
  5. If fill valve is corroded or damaged, install a brand new replacement valve. Ensure it is sized for your toilet model.
  6. For less severe issues, install rebuild kit components per manufacturer instructions. Clean piston, diaphragm etc.
  7. Reinstall fill valve into tank and secure with mounting nut. Reattach water supply line.
  8. Turn on water and allow tank to fill. Adjust float cup height as needed to achieve proper shutoff at correct level.
  9. Flush toilet and observe fills. If running continues, further fill valve adjustments or replacements may be necessary.

With a fully functioning, well-sealing fill valve, the tank will shut off water properly once full. This prevents overflows and waste from a constantly running toilet.

Repairing Leaks from Loose Tank Bolts

The tank bolts securing the tank to the toilet bowl can loosen gradually over time. This allows water to drip down the bolt holes onto the floor around the toilet base. Before this leak causes bathroom or ceiling damage below, take steps to tighten or replace the bolts:


  • New tank to bowl rubber sealing gaskets
  • Tank bolt set
  • Adjustable wrench
  • Terry rag
  • Silicone sealant


  1. Turn off toilet water supply. Empty tank. Place rag beneath bolts to catch drips.
  2. Hold tank steady and use a wrench to loosen the nuts on each tank bolt below the bowl.
  3. Fully loosen and remove loose, corroded bolts along with old sealing washers.
  4. Apply silicone sealant to underside of tank and bowl rim where they meet.
  5. Insert new rubber sealing gaskets over ends of replacement tank bolts.
  6. Slide bolts through toilet tank holes to bowl slots. Thread nuts onto bolt ends.
  7. Tighten nuts carefully and evenly so tank pulls up flush to bowl. Do not overtighten.
  8. Turn on water supply and allow tank to fill. Check under toilet for any drips. Retighten bolts if needed.
  9. Let silicone fully cure 24 hours before using toilet. The fresh seals and tightened bolts will prevent leaks.

With tank bolts properly secured, no water can leak through the connections down onto the floor. This prevents damage and the need for more extensive repairs later on.

Fixing a Leak from a Damaged or Disconnected Flush Lever Chain

The thin metal or plastic chain linking the flush lever handle to the flapper is another potential source of leaks in pressure-assisted toilets. Over time, the chain can become disconnected, preventing the flapper from fully sealing. Or corrosion can damage the chain so it no longer pulls the flapper open all the way.

Adjusting and replacing this small but crucial chain takes just minutes:


  • 3/8″ flush valve chain
  • Needlenose pliers
  • 1/4″ nut driver


  1. Remove tank lid and set aside. Locate chain connection on flush lever and flapper.
  2. Use pliers to detach old chain from corroded retaining nuts or clips at lever and flapper. Remove chain.
  3. Assess required new chain length to allow slack when flapper is closed, but goes taut when lever is pressed.
  4. Attach one end of chain through flapper hole with chain clip. Secure with retaining nut.
  5. Attach opposite end of chain to flush lever hole. Adjust slack so 1/2″ of chain drapes loosely.
  6. Secure chain to lever with nut. Verify chain pulls flapper fully open when lever is pressed.
  7. Operate flush lever and observe flapper movement. Readjust chain slack if needed for complete flapper motion.
  8. Replace tank lid. Turn on water supply and flush toilet, checking for proper lever/flapper function.

Taking a few minutes to detach, inspect, and reconnect a damaged lever chain can return your pressure-assisted toilet’s flush to full functioning. A properly rigged chain is essential for carefree flushing.

Preventing Future Leaks

While all toilet components will wear out over time, you can maximize the leak-free lifespan of your pressure-assisted toilet with some simple maintenance:

  • Inspect flapper, chain, and seals every 3-6 months. Replace components at first sign of damage or wear.
  • Clean fill valve and overflow pipe regularly to prevent clogs. Scale buildup can impede proper valve closure.
  • Always use manufacturer approved replacement parts designed for your specific model.
  • Ensure bowl is level and tank/bowl are aligned properly to allow even seal compression.
  • Avoid exposing tank components to cleaning products. Stick to water and baking soda solutions.
  • Shut off water supply and drain tank before lengthy vacations or absences to avoid leaks while away.

With regular inspections and maintenance, you can catch most pressure-assisted toilet leaks before catastrophic failure occurs. Know the unique leak points and repair procedures, and you can stop running toilets in their tracks.

Common Questions About Pressure-Assisted Toilet Leaks

What if water keeps leaking after I replace the flapper?

  • Ensure you are using the precise replacement flapper for your toilet model. Improper sizing can allow leaks. The overflow tube height inside the tank may need adjustment for proper flapper sealing as well.

Why does my toilet run periodically even though I don’t see constant leaks?

  • Intermittent running is usually caused by a slightly misaligned or warped flapper that isn’t making a watertight tank seal after flushing. Replace the flapper. Check that the flush valve seat is clean.

Can I patch a crack in my plastic pressure vessel?

  • Unfortunately, most pressure vessel leaks or cracks cannot be reliably repaired. The compromised air and water pressure tight seal makes patches very prone to failure. Complete pressure vessel replacement is recommended.

My toilet leaked a brownish water from underneath. What caused this?

  • Brown water leaking from beneath your toilet indicates a corroded, rusted tank bolt. The rust and sediment has dissolved into the tank water. Simply replacing the tank bolts and seals should fix this leak issue.

Why does my toilet hiss or run briefly after flushing?

  • Slight hissing or running after a flush is normal in pressure-assisted toilets. This is the sound of the pressure tank repressurizing. However, extended hissing or running indicates a leak is present allowing water to continuously flow from tank to bowl.


Dealing with any type of toilet leak can be frustrating. But armed with the right information and tools, fixing a leaking pressure-assisted toilet is very manageable. The key is pinpointing the leak location, then using the proper repair steps outlined here to address each specific issue.

With parts like flappers, gaskets, and fill valves costing less than $10 each,