Required Tools: Needle nose pliers, Phillips and slotted screw drivers, heat sink compound (or thermal grease) and a battery powered voltmeter.
WARNING: To avoid electrical shock, make sure that all of the power is off to the heater before attempting to remove the old control board and while installing the new control board.
Turn off all the power to the heater. Confirm the power is off with a voltmeter, even if the status light (or LED) on the control board is off. There may be multiple breakers powering your model heater.
You may want to label the incoming power wires to make replacement easier and to avoid installing them out of phase or out of sequence. With a slotted screw driver, remove the power wires from the screw lugs on the right hand side of the board.Using a pair of needle nose pliers, pull all of the control wires off the spades on the circuit board. Be sure to pull on the connector, not the wire.
Figure: Control board power lugs (L1 & L2) and the triacs attached with Phillips head screws
Using a Phillips head screw driver, unscrew the triacs from the heat sink to the right of the board. Take care that the screws are not lost, they will needed for the new board.
Using a Phillips head screw driver, remove the four mounting screws from the board, be ready to support the board as you remove the screws. Be careful not to get the white heat sink compound on your clothing, as it is difficult to wash out.
Place heat sink compound on the triacs being careful not to bend the leads. Be sure to get a thin coating covering the entire back of the triacs, if you don’t, they will burn out as soon as you power up the heater. To maximize thermal conduction, it is advisable to clean the backs of the triacs with alcohol before applying the heat sink compound.
Loosely mount the board to the heater with at least two Phillip head screws. Screw the triacs down to the heat sink; be sure they are flat against the heat sink. Don’t twist the head off of the screw, if you feel any resistance, back the screw out and try again.
After the triacs are snug, tighten down the board screws (8 in.-lbs.). Don't tighten them so much that you bend the board.
Replace the main power wires into the screw lugs and tighten. If the wires are stranded, make sure all strands are in the lug to avoid possible shorting of the control board.
Replace the control and element wires (see schematic inside the protective cover).
Using the "Matching Procedure" above, match the control to the thermistors and place the heater back in service.