Our website uses cookies to ensure a better performance and to measure page visits. Find out more about our use of cookies or how to change your settings, delete or turn off cookies at any time. Otherwise, we'll assume you're OK to continue with cookies in use. Accept

Thermostat/ controls Thermostat/ controls

Summary

  • Failure mode Thermostat or other electronic control faults can lead to temperature variation and poor cooling of contents.
  • Durability feature Specification and testing for longer life of components, PCBs and connectors and accessibility for easy replacement.
  • Cost

Good practices

  • Good practicesNTC thermistor control
  • Good practices Soldered connections
  • Good practices Surface mount components
  • Good practices Quality control procedures
  • Good practices Environmental testing of PCBs

Bad practices

  • Bad practicesNon NTC thermostat
  • Bad practices Spade/tab type connectors
  • Bad practices Through hole components
  • Bad practices No PCB quality control
  • Bad practices No PCB environmental testing

Key facts

  • Which? Consumer surveys indicate some of the most common faults relate to bad smells, mould and leaks. 
  • Around 1 in 3 of all fridges replaced in the UK each year failed to meet customer’s expectation for an 8 year product lifetime. 
  • Which? surveys show that the most common faults are build-up of ice, blocked drain and flooding in unit.

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 and later in lifetime

Temperature controls (thermostats) and other electronic controls can fail at any time in the life of a fridge-freezer for various reasons, including poor components and manufacture, and due to the thermal cycling and occasional vibration they may suffer inside the unit. 

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.

Thermostat type and connectors

  • Negative temperature coefficient (NTC) thermistors to be used.
  • Soldered connectors to be used where this will not inhibit replacement of PCBs/key parts.
  • Thermostat and all PCBs to be easily accessible to remove/replace and available in the UK at reasonable cost for at least 5 years after the machine was last manufactured.
  • Replacement control PCBs to be available pre-programmed or are able to be configured from the board itself. Any reprogramming software to be made freely and publically available.
  • Quality control procedures to be in place/documented for above characteristics

PCB quality and inspection

  • Thermistor, control chips and other key components to be surface mount on all fridge freezer PCBs where possible.
  • Thermostat control PCB to be conformally coated with an acrylic or silicone.
  • Where electrical connections are not soldered, gold-plated connectors to be used rather than tin-plated to prevent fretting.
  • All PCBs to comply with IPC610E and IPC-J-STD-001 concerning PCB build quality

Environmental test standards

  • PCBs/circuits to meet relevant environmental test standards noted below *.

* Environmental testing should be undertaken by an independent laboratory to:

Relevant test methods include EN 60068-2-6:2008 (environmental testing Part 2-6:  Test Fc: Vibration (sinusoidal)) and EN 60068-2-64 (environmental testing Part 2-64: Test Fh: Vibration, broadband random) for vibration resistance for circuit boards. Connectors can be tested using the methods in EN 60512-6-4 Connectors for Electronic Equipment - Tests and Measurements - Part 6-4: Dynamic Stress Test 6d: Vibration (Sinusoidal).

Testing to demonstrate performance

The thermostat should be tested for 75,000 cycles (seven year lifetime). Test conditions should reflect IEC 60335-1:2013 and be carried out at ambient temperature.

The heater and controls should last 2 500 cycles (~7 years), in line with the UL 250 (Canadian standards for Household Refrigerators and Freezers) Clause 8.20.1.

Ask for clear evidence of meeting the requirements listed above, e.g.:

  • technical specifications, drawings, photographs; test data, quality control data

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).

Saving

Neutral

NTC thermistors
These give more efficient and reliable control of temperatures in the fridge freezer.

Inspection procedures
Simple inspection procedures will help to identify manufacturing faults and component issues, reduce failure rates and customer returns.

Accessible / Replaceable Parts
Accessible and replaceable thermostat parts will reduce the cost and increase probability of replacement

Low cost

Surface mount and conformal PCB coatings

Surface mount and conformal coatings will increase life and reliability of PCBs.

Gold-plated connectors

Gold plated connectors increase the reliability of PCBs.

PCB inspection and environmental testing

Additional testing and inspection of circuit boards will help to reduce failures and increase reliability and life of these components.

High cost