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Knowledge document #3452
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Batteries in FRITZ!DECT radiator control drain quickly

The batteries in FRITZ!DECT 301 go dead after just a few days or weeks. The battery level displayed for the radiator control in the FRITZ!Box user interface is low. If the push service is enabled, you also receive emails notifying you that the battery is low.

Note:The battery level displayed is only an approximate value based on the open-circuit voltage. Since battery status reports are sent early on, you can usually use the batteries for several more days. Under normal conditions of use, the radiator control's batteries last for at least the duration of one heating period; however, the actual service life depends on the switching cycles, movability of the valve, and the use of manual functions such as the boost function.

Note:All instructions on configuration and settings given in this guide refer to the latest FRITZ!OS for the FRITZ!Box.

1 Updating the firmware of the radiator control

  1. Click "Home Network" in the FRITZ!Box user interface.
  2. Click "Mesh" in the "Home Network" menu.
  3. Click "Perform update" next to the respective device.

2 Using high-quality batteries

  1. Do not use rechargeable batteries in the radiator control. Rechargeable batteries usually have a higher internal resistance and a higher self-discharge rate than disposable batteries and produce lower voltages. This can affect how the radiator control functions and shorten operating time.
  2. Do not use zinc-carbon batteries. Due to their construction, they are not suitable for use in radiator controls.
  3. Use high-quality batteries! Varta Industrial Pro AA, Varta Longlife Max Power AA, GP Super Alkaline LR6, or Duracell Industrial AA are suitable.
  4. Do not mix used and new batteries.
  5. Make sure that the batteries are firmly seated between the battery springs.

3 Check the movability of the radiator's valve pin

If the radiator's valve pin cannot move freely due to calcium buildup that accumulated during the summer season, the radiator control's battery may drain more quickly. The valve pin is a small, nail-shaped pin on the radiator that usually sticks out a few millimeters.

  1. Remove the radiator control.
  2. Carefully open and close the valve pin on the radiator a few times, for example by pressing it with a coin or carefully pulling it with pliers. If necessary, you can also use a drop of machine oil.
  3. Remount the radiator control as soon as the valve pin can move freely and smoothly.

If the battery still drains quickly and you are not sure whether the radiator's pin valve can move freely enough, you can also mount the respective radiator control on another heater for testing purposes.