This is the over view of my project that dose more then just the heating but I will try to explane the heating control side
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Step 1: THE HARD WARE
raspberry pi B as the many controller
two of the relays to control the switching of the boiler
4x 1wire DS18b20 temp sensors
and a conversion board to control the relays 5v logic with pin points to connect the sensors
Step 2: THE CAYENNE APP
Using my devices with cayenne app on my phone is easy to crate schedule's and trigger points for high or low temp and even monitor each zone ,
and using the online dash to over ride the relays is made easy.
Step 3: How It Works
with the cayenne app scheduler widget one of the relays will only switch between set times and with the trigger widget the second relay will only switch if the temp drops to the set trigger point.
So using the sensors in each room I can set individual low and high trigger points so if the temp drops in one the heating will switch on and if it gets too high in another it will switch off only between the set time.
and running the relays in series with both the schedule and trigger widget they both need to be switched before the heating comes on.