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Water gauge window and watertight seals Water gauge window and watertight seals


  • Failure mode Water leaks can occur from the water level window.
  • Durability feature Good design and quality control can address leaks.
  • Cost

Good practices

  • Good practicesSuitable material selection
  • Good practices Tight tolerances

Bad practices

  • Bad practicesLarge gaps in base
  • Bad practices Incompatible body and window plastics. This will be identified when kettles are tested
  • Bad practices as they will leak

Key facts

  • The return rate can be as high as 30% for a bad design.
  • 22% of consumers check on-line reviews before buying to avoid unreliable brands.

Icon key

  • Failure mode Failure mode
  • Durability features Durability features
  • Cost saving Cost saving
  • Low cost Low cost
  • Cost neutral Cost neutral
  • High cost High cost

Key failure modes

Early to later in lifetime

Water leaks are one of the most common causes of early returns and mainly occur from the water gauge window, but can also occur at the seal between the concealed element base and bodies.

Leaks from the bond between the water-level viewing window and the body:

  • With plastic body kettles, the plastic windows must be bonded to the plastic body by ultrasonic welding as “food grade” adhesives are not suitable in steam.
  • Ultrasonic welding is an effective method for bonding two pieces of one type of polymer as long as suitable grades are used and the bonding process is carefully controlled.
  • Viewing windows in metal body kettles are made from tight fitting plastic inserts that have sealing membranes, which are “snapped” into gaps in the steel body. The dimensions of the insert and orifice must be precise to avoid leaks.
  • Plastics expand more than metals when hot so the insert should become tighter in the metal space as the water heats up, but it must not distort.

Leaks at base:

  • Concealed kettle element plates are sealed in plastic kettles with silicone rubber gaskets that form a tight seal. Proprietary seals are available. Concealed element plates are welded to metal body kettles. 

Specification for improved performance

The specification below provides the recommended improvements needed to improve product durability. Specifications are ranked from bronze to gold based on the effectiveness of the change in improving durability, with bronze being the minimum recommended.

Test new designs to ensure they survive required number of cycles

Plastic kettles

  • Use compatible grades of plastic suitable for ultrasonic welding.
  • The shape of the bond between body and window should not be simple flat surfaces, and most factories use proprietary designs that have more complex shapes that maximise bond area.

Metal kettles

  • The dimensions of the space in the steel body and the plastic window insert must be precise to avoid leaks.
  • The plastic insert must be very tight in the gap in the kettle body and must not distort in use.

Kettle base

  • Use suitable silicone seals to form watertight bonds for plastic kettles. Suitability of watertight bonds are checked by testing.

Testing to demonstrate performance

  • Request test samples to check resistance to leaks
  • Kettle testing as described for lids will also test kettle seals. The test used is fill / boil / empty with lid opening and closing and carried out for the required number of cycles. Descale as necessary during test. 

Cost implications

Improved reliability of components can reduce early returns and improve brand reputation which, in turn, can lower business costs and increase long-term sales.

To calculate overall cost savings for your business, use the WRAP cost/benefit analysis tool (currently in draft form and available on request).



New design testing

Testing will identify fatal flaws. Independent kettle design assessment and durability testing can be obtained free of charge from some manufacturers of kettle controls if sales volume are sufficiently high.

Quality control Good quality control and change control should be standard procedures in factories.

Low cost

High cost