The Automix 30 is an electronic thermostat that adjusts the water mix valve for a floor heating system. It has sensors for outdoor temperature and the temperature of the outgoing waterflow to the floor heating system and adjustable parameters for heat curves, offsets, minimum and maximum water temperatures. There are some simple ways of doing a temperature setback at night (or multiple timers depending on exact model), but there is only one setback temperature not can it be easily remotely controlled. The sensor for the supply water is a PTC thermistor with a resistance of about 1000 ohms at 25°C (and increasing by about 7.8 ohms per degress). With a simple relay board and some extra resistors (trim potentiometers) we can do more flexible setback temperatures with e.g. an Arduino (or a Jeenode that I prefer). The schematic contains a total of three relays. Two of the relays can cause an extra resistance to be added in serial to the temperature sensor, i.e. the Automix will be fooled into thinking the outgoing water temperature is too high and will lower the temperature by a corresponding amount. The third relay can connect a resistance in parallell to the sensor in order to cause a raise in water temperature. If the increases and decrease of apparent sensor resistances are adjusted to correspond to changes in water temperatures of -1°C, -2°C and +4°C respectively, the floot heating can be adjusted freely between -3°C and +4°C in whole centigrade steps by activating any number of relays on the board. The relay board needs a supply of +5V for the relays, but the relays can be actuated using 3.3V signalling from a Jeenode. This design has been built and tested to work exactly as expected!