Unfortunately any electronic thermostat is subject to fail eventually. Many of the commonly used thermostat have mechanical relays which will cycle frequently when maintaining a tight temperature range in incubators, resulting in a short service life. The addition of a secondary wafer thermostat in addition to the primary digital type will protect the egg from overheating. I use industrial type PID temperature controls which are remarkably reliable, accurate and stable. They are not plug and play type units and require a separate Solid state relay, temp sensor and must be wire together. They also will need to be setup and calibrated, but have autotune functions which adjust to different applications. Cost me around 100.00 for quality components. At times I use a secondary wafer thermostat just as a precaution as they are more resistant to current surges that can damage electronic components. If your are more comfortable with plug and play types, try and find a unit that has solid state switching rather than a mechanical relay. The switch in the photo Is used to temporarily bypass the controller so I can adjust the over temperature set point of the wafer thermostat independent of the digital controller.
