Inside my boiler is a Grundfos switch with a dial for numbers 1/2/3. the boiler works fine when this is on 1 but if i switch it to 2 or 3 (which i assume will make the water hotter) the boiler will not turn off if i run the central heating. it just constantly stays on burning. However if i turn off the downstairs radiators it goes back to it's stop-start usual self. The problem also is that the water does not get any warmer with the switch at 2 or 3.
Does this dial control the water temperature? or any clues as to how i would sort it out... many thanks guys