You are in the wrong thread. This should be in heating.
What is your outside temp for a start.
Also the way temp control works is that say your target is 18.5 then the temp won't switch off at exactly 18.5 it will normally switch off when the temp is say 19.5, normally this over temp level can be set up, sometimes it is referred to as Hysteresis. Last heating system I worked on for a client, you could set this over temp from between 0.5șC to 5șC the default was 3șC, and there was a separate under temp setting . You may want to check this out. So if the under temp is set to 2șC then the heating won't come on again until 16.5șC. If you set these temps to 0 or too low then your heating system will always be on, as its trying to fight with itself to maintain the temp.