how can i fix my vokera linea 28 boiler?

I have a linea plus ,on the plus and 28 the main flow switch is below the pump on the left of center it is round with 3 screws holding it in place the micro switch then sits on top of it fixed with one screw.
when the boiler starts up the center pin should push on the micro switch.mine was all cloged up so cleaned it and put back it works but still have a problem with boiler going to burner overheat.
Before you remove the flow switch you MUST switch off the electricity, and drain water from boiler.
Turn off cold supply to boiler,black knob on right side reach up under boiler.Then turn flow and return valves in to off position(pipes on left side, line on tap horizontal) Then find safety valve which behind a black plastic box which has a lead coming out of it.Hanging down from the safety valve is a strip of plastic if you pull this water should go through the safety valve to the out side of the building.Before removing the valve check to see if water pressure is now Zero,if not you need to check every thing is off.

stuart
November 2009