I've no idea but after trial and error I've left the heaters as no. 5 and no. 6, 6 being heat level. I also had to test the switches on the fuse box over a couple of weeks. After a couple of weeks on various settings / switches I have managed to have heat come on in the morning and stay on at a comfortable level all day and evening. I don't think you can arrange to have the heat come on at say 5pm.