This should be completed by qualified technician only. This guide is meant to be a supplement to the replacement instructions included with the LGM circuit board.
Remove the outer white cover and make sure power is turned off to the boiler.
1.) Unlock the little white (or sometimes red) clips (2) on each side of the control console and slide
the console off. Set aside.
2.) Remove the pressure gauge that is snapped into the control and move off to the left side.
3.) Loosen the 2 screws holding the control to the boiler and slide the control out and down to
expose the top of the console.
4.) Remove the clear drip cover with the small screw in the center. This will require a T10 bit included in the Viessmann service tool kit.
5.) Remove the small top front cover using a flat tip bit to gently pry off.
6.) Loosen the 2 screws on the top back cover, one each side, and remove.
7.) Loosen and remove the 4 screws on the main body cover that are located 1 on each side and 2
along the top. Unplug the green ground wire and allow to pull through the provided slot.
Remove the cover to expose the LGM circuit board. Be careful to allow the smaller VR20 circuit board to slide in the slots in the body of this cover.
8.) Unplug all of the plug in connectors along both the top and the bottom of the circuit board.
Move them out of the way to allow removal of the circuit board. All of the plugs are numbered and labeled and correspond to a specific position on the circuit board which is also labeled accordingly. The only two plugs that are similar are the orange X6 and X7 plugs along the bottom, which are also labeled to assist if needed.
9.) Carefully remove the smaller VR20 circuit board that is plugged into the LGM 29 board using the supplied metal handle that fits into holes on the top edge of the board.
10.) Loosen and remove the 5 screws that attach the LGM board to the control. The screws are
located 3 along the bottom, 1 in the middle, and 1 in the upper right corner. 11.) Install the new replacement LGM board and attach using the 5 screws. Make sure to check the red dip switch settings on the replacement LGM board as they correspond directly to a specific model of boiler. Adjust as necessary according to manual provided with the replacement LGM board.
12.) Reinstall the VR20 circuit board and reassemble all of the control covers in the reverse order in which they were removed. Remember to route the green ground wire through the slot
on the main cover.
13.) When sliding the control console into place it is important to align the console bottom
edges with the slots along the side in the holder to allow for the small clips to attach the console
to the control. Push in slightly on the sides to allow console to seat completely in the holder and
fasten white or red clips.
