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Lid closure mechanism Lid closure mechanism


  • Failure mode Failure to stay closed or failure to open due to unsuitable materials or design.
  • Durability feature Durable materials and good design can help address
  • Cost

Good practices

  • Good practicesUse suitable grades of good quality materials
  • Good practices Test new designs

Bad practices

  • Bad practicesAvoid sub-standard plastics - which is often due to too high a % of regrind being used
  • Bad practices Avoid sharp angle in mouldings

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

Poor lid design, sub-standard materials and poor construction can let steam escape and prevent the kettle from turning off (and risk burning your customer with steam or spray).

Most designs rely on plastic levers to open and close latches that hold the lid shut. These sit below a lip at the top of the kettle body to hold the lid shut and when withdrawn, the lid is released.

  • Failure occurs due to fracture or distortion of plastic parts.
  • Sub-standard plastic (e.g. too much regrind) used for the kettle body can distort when hot.
  • Metal body kettles usually use the same types of plastic lid closure mechanisms as plastic body kettles.
  • Failure can occur  within a few weeks or later in life and depends on the design

Failure to open

  • Plastic parts with too much regrind can soften and distort, when hot.
  • Latches do not move enough to disengage with the lip of the kettle body when the lid opening button or lever is pressed. Distortion can also cause excessive steam release.

Failure to stay closed

  • Protruding plastic rods in kettle lids, such as in the image below, that act as pivots to allow levers to rotate, can form cracks at sharp angles in the moulding. These cracks grow and cause breakage of the plastic parts.
  • Another cause is distortion of the plastic levers made of unsuitable or sub-standard materials which no longer protrude sufficiently to engage with the lip. A less common cause is poor quality mouldings that break under stress.

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.

Good design; suitable choice of types of plastic and quality; maintain production quality

Durable plastics

  • Lids will open and close properly if suitable plastics are used and are a good robust design. Ensure that the quality and grades of all plastics used for kettles is suitable and that sub-standard contaminated plastics are not used
  • Preferred types of polymers can be specified. These include nylons (polyamide), PPO or POM.
  • Long reliable life requires robust plastics that do not distort at 100˚C (boiling water), they need to be able to slide across other surfaces with minimal friction resistance, and they must not be susceptible to fracture when under strain.

Good design

  • Sharp angles should be avoided, and if this is not possible then a fracture resistant type of plastic should be specified.

Production quality

  • Fully testing prototype new designs to ensure good reliability and then ensure that the same parts and materials are used for production. No changes are permitted without retesting and permission from the buyer. Ask your local technical team to monitor production quality.

Testing to demonstrate performance

Brands and major control suppliers, such as Otter and Stryx, routinely carry out kettle durability testing. Major control manufacturers also test control mechanisms and may provide kettle design advice and kettle testing services. This may be at no cost for high volume projects but there will be a charge for lower volumes.

  • Test method: “fill / boil / empty” with lid opening and closing and this is typically carried out for up to 20,000 cycles for kettles with concealed elements and 6,000 cycles for coiled immersed elements.
  • A good design with concealed element will survive 20,000 cycles which is equivalent to about 7 years normal use.

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 defects. 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 kettle factories. Your local technical team can monitor quality.

Low cost

Specific grades of plastics

There will be an additional cost for using higher priced engineering polymers with superior performance at 100˚C but this should reduce early returns. Testing will confirm if durability is improved

High cost