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