Conrad FS20 IRP Bedienungsanleitung Seite 37

If not all expected data was received and if there was no transmission error, the FS20
transmitter remains in programming mode for approx. 1 minute longer and waits for further
data.
In both cases, you can repeat programming after exiting the programming mode.

Note:
The "FS20 S4U" does not have a status LED; therefore no signal is emitted
during programming as described above. Make sure to press the keys "2" and
"4" (see operating instructions for the "FS20 S4U") for 5 seconds. After
programming, you can verify its success by simply testing the "FS20 S4U".
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