Diagnosing a Bad Control Board vs Transformer

Before replacing an expensive control board, learn how to diagnose whether the board or the 24V transformer is truly at fault.

Use a multimeter to diagnose:

1. Check for 24V at transformer secondary terminals.

2. Check for 24V at R and C terminals on the board.

3. Check for 24V output at Y, W, and G terminals when calling.

4. A board with no outputs but correct inputs is failed.

5. No input voltage points to transformer or wiring issue.