can anyone help me i am trying to understand my central heating the flow and return for the rads are on pump side of my boiler the hot water is on the right side with no obvious link to pump and their is no two or three way valve or tank stat but on my control i can only turn water and heating on / and heating off water on and there is a room stat fited .the hot water is on 28mm pipes and heating on 15mm pipes to upstairs and 10mm down conected to manifold would be gratefull for any comments thanks