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Steam pipe Steam pipe


  • Failure mode Kettle too slow to switch off which can lead to early returns.
  • Durability feature New design testing can be obtained free of charge.
  • Cost

Good practices

  • Good practicesEnsure unrestricted flow of steam
  • Good practices Test new designs

Bad practices

  • Bad practicesUse of unsuitable plastics for kettle body or lid

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 life

  • A common complaint is that new kettles take too long to switch off and result in early returns. After a short period of use, this time can lengthen and eventually they do not switch off at all.
  • Switch off time is a function of the overall design of the kettle. The time for steam to reach the bimetallic strip depends on the design and location of the steam pipe which needs to allow free flow of steam but avoid blockage by scale build up.

Causes include:

  • Poor kettle design, especially the design of steam pipe, the shape and size of the spaces at the top and at the bottom that must allow unimpeded flow of steam.
  • Sub-standard plastics used for kettle which distort causing gaps at the lid and spout so that steam escapes instead of passing down the steam pipe (see also Lid Failures).

Later in lifetime

Switch off times will increase if scale builds up in or around the steam pipe or if a gap develops between the lid / spout and body which releases steam.

Specification for improved performance

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

Test new design

Switching off requires the water to boil so that steam is forced down the steam pipe to the bimetallic strip. Heat causes the strip to “trip” the electric contacts to cut off power. Anything that hinders steam flow will delay switch off time.

  • Steam pipes are usually made of metal (polypropylene can be used) so that they get hot as the water is boiled to avoid cooling of steam inside the pipe.
  • The kettle lid and spout must be well sealed so that steam is forced down the pipe. Ensure grades of plastics used are suitable so that no distortion occurs at 100˚C.
  • The dimensions and shape of the pipe and the parts at the top and the bottom are important to ensure unrestricted flow of steam. Any water in the pipe must be able to escape. The top of the pipe needs to be close to the kettle lid and designed to avoid splashes of water depositing scale in the pipe.
  • The time between the start of boiling and power being automatically switched off can be specified (e.g. <10 seconds). The specification must include: 
  • Maximum time at all fill levels of the kettle.
  • That this time is unaffected (for at least the warranty period) during kettle testing with hard waters that cause scale deposition.

Testing to demonstrate performance

Kettle testing as described for lids can also be used to ensure that kettle switch off times do not become too long in use.

The test used is fill / boil / empty with lid opening and closing and this is 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.

Low cost

High cost