You can definitely set the channel. I assume it uses a default channel if you don't set one manually. There's a scanner sketch for the Arduino, maybe the Pi too, which shows interference on each channel.
And my heating didn't come on at the start of the week. I tried loading my web interface and it said "Can't connect to boiler :(" I thought something was broken but the radio connected to my Pi had slipped down the side of my subwoofer behind the telly and blocked the signal.