Tried that! Several people, including two young plumbers, have all been sure they could do it, to no avail. It can either be on all the time or off all the time!
I don't have customers, I am nearly seventy, and haven't been fit enough to work since I was 59! I am just putting my hand up, saying I am not able to work this out and asking for help.
We moved into this house five months ago, I was a qualified plumber and have fitted many heating systems, but cannot get this system to operate correctly. It is controlled by a promgrammable room stat, which is a VRT340F. I have spoken to Valiant and downloaded their instructions, it still does...