How to determine if a toilet fill valve seal needs replacement?

The key to determining whether a toilet fill valve seal requires replacement lies in identifying abnormal symptoms related to seal failure. A diagnosis can be confirmed through visual inspection and simple testing, specifically by assessing the following five critical aspects:

I. The most typical indicator: Continuous “running water” from the toilet tank (easiest to detect)

This is the primary indicator of seal damage, manifesting in two scenarios:

- The tank water level appears normal, but a constant “hissing” sound of water filling can be heard (the valve continuously replenishes water), causing water to flow through the overflow tube (the vertical pipe inside the tank) into the toilet bowl, leading to unexplained increases in water bills.

The tank water level remains persistently high, even overflowing the tank rim. This occurs because the seal cannot block incoming water, preventing the fill valve from closing completely. Water continuously fills the tank and must escape through the overflow tube or over the tank rim.

II. Visual Inspection: Physical Damage to the Seal Ring

Lift the toilet tank lid and locate the fill valve (typically on the left side of the tank, connected to the water supply line). The seal ring is usually found at the bottom of the fill valve where it connects to the tank, or inside the valve core as a rubber/silicone ring (often black/transparent and soft). Directly inspect:

- Surface cracks, tears, hardening due to aging, or deformation (rubber loses elasticity over time, failing to conform to the sealing surface);

- Whether the seal has fallen out or shifted position (misalignment prevents sealing);

- Severe mineral buildup or stubborn stains adhering to the seal surface (causing an uneven sealing surface, preventing sealing even if undamaged).

III. Auxiliary Test: Water Stop Performance After Closing the Inlet Valve

If unsure whether the seal ring is the issue, perform this simple test:

Close the toilet's angle valve (the small valve on the wall connecting to the inlet pipe; turn clockwise fully to stop water flow);

Observe the tank water level: If the level stops dropping and no continuous running sound is heard, the problem is likely in the inlet valve (including the seal ring) — because closing the inlet cuts off the “leak source”;

If leakage persists after closing the angle valve, the issue likely lies with other components (e.g., the flush valve seal), ruling out a faulty inlet valve seal.

IV. Other Indirect Indicators

Intermittent tank refilling: After flushing, when the tank refills, the water level stops just as it reaches the set height. However, after a short while, it begins to refill slightly again, repeating this cycle (caused by incomplete sealing of the gasket, leading to leakage when water pressure fluctuates).

Water seeping from the inlet valve connection: If water drips from the joint between the inlet valve and the tank bottom (not from the inlet pipe fitting), it may indicate seal failure due to aging.

Summary: Replace the seal directly if any of the following occur:

- Continuous tank refilling (with hissing sound) or abnormally high water level;

Visible cracks, damage, hardening, or displacement of the seal ring;

Persistent leakage/abnormal inflow after descaling the seal ring surface.

Note: Seal rings are consumable parts (rubber material typically lasts 3-5 years). Replacement is inexpensive (under several dozen yuan). If damage is uncertain, replace directly (simple installation requires no specialized tools) for greater efficiency than repairs.