The HomeMatic range of home automation products are excellent value for money. I have had them in service in my home for 10 years. Recently, I came home to a very, very warm living room. My HomeMatic thermostat was showing an F1 error message. This means that the valve must be sticking, making temperature adjustments impossible.
Now, sticking valves are a common thing in radiators. After a summer of no movement they tend to stick at the beginning of winter. Removing the temperature adjustment knob and banging the valve head with a hammer is usually all that is needed to free things up.
Attaching it to my lab power supply showed that the device was drawing 300 mA whilst doing nothing. That is way too much for one of these extremely low power devices. So the case was opened to see if the gear-box was sticking and causing the electric motor to draw excessive current.
The mechanism was taken apart and inspected. It turned freely and without any issue. So a deeper inspection of the electric drive components on the circuit board was necessary.
The board was pulled and instantly a component fell out into my hand.
This component was at one time soldered to the RFK1 board behind it. So it was resoldered into place and the unit powered up again, however, this time the display on the thermostat showed a "trd" error message. Upon reading the documentation, I saw that this means the transciever module was not working.
I am guessing that the component on the RFK1 board contained loading coils for the antenna. Once they fell off, the SWR went high and burned out the RF circuits.
No repair for this one.
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