Siemens Rdj10RF timer?

Just had Siemens thermostat fitted Friday, the plumber told me to read instruction to work it, but he'd left the radiaters on and said just turn the controller knob right down to turn off and turn back up to turn on, with out useing or setting the timer, the day after I came to turn the controller up to turn radiaters back on and didn't work, so tried setting timer and that didn't come on, didn't work until I pressed the over ride button on the recieved, what am I doing wrong to sett it up with the controller to come on please someone help.