After to many hours of trying to get my fibaro system and horstmann/secure getting to work here a howto what worked for me:
1. Install the relais and the thermostat separate to the fibaro system (don't connect the devices to each other as the manual suggest)
2. Include the thermostat using the include mode on the thermostat (dip switch to 1 to on and turn wheel to I and press)
3. Include the relais by
a. first remove device in fibaro system and press network button on the relais
b. include the relais by getting fibaro in include mode and press the network button on the relais
The relais and the thermostat works with fibaro (change the wakeup time to 256 for the thermostat by change it in fibaro and put thermostat in install mode (dip switch 1 to on) and toggle the wheel to the n. You can manipulate both relais and thermostat temperature.
Last step is associate the thermostat to the relais, by using fibaro (straightforeward connection).
When using a normal HCV (like Nefit) you can turn on the HCV by shorten the signal wires from the HCV to the relais. Use connector 2 and 4 for this. And check with a multimeter. On = 0 ohm resistant, off = Unlimited resistant.
This should do the trick, create heat scenes etc for correct working.
One thing I noticed, when changing the thermostat temp and turning the boiler on, the change state is not visable in fibaro.
Good luck with the horstmann/secure thermostat!