OFCH controller

caz2703

I hope this is the right board for this query - please move if I messed up!

I currently have a Horstmann 425 Diadem controller for heating & water and would like to upgrade to a digital controller with more provisions than I currently have but I'm confused by the current set-up.

At present the selectors are interlocked but it doesn't make sense. The interlock on the water is vertical and on the heating it's angled. The manual suggests that a gravity system where water can be on independently of heating, the interlocks would be the other way around yet I know that during the summer, I had hot water but no heating and now in the winter, I have to have both HW & CH on for the heating to work. My controller is set up with the interlocks opposite to that in the following link for gravity systems: http://www.manualslib.com/manual/475151/Horstmann-425-Tiara.html?page=5#manual

Is this a problem I need to get a professional out for before I buy a new controller? Aside from that, can anyone recommend a new controller based on the above? I would like to be able to program each day differently and have the ability to boost the heating for 1 or 2 hours as well as change to on or off. The handyman employed by the agency I lease from seemed to think that I could get any old controller and he could fit it. I'm not sure if I need a second opinion and if so from which trade - electrician or plumber?

Many thanks for reading.