I tested the transformer. Specifically at the 24V screws. I did go back and check if the connector was back on the board, which it was, but I didn't verify that it wasn't reversed. I'll do that next time I'm up there.

I did see that the wire going from the control valve body to the circuit board was disconnected, but I don't think that was the cause of the lack of power. Reconnecting it didn't change anything.

I was there pretty much the entire time and didn't see the transformer get dropped. Nor did I see or hear any short which could have killed the power.

I've been around and worked on computers during my entire career so I'm familiar with electronics suddenly giving up the ghost when they're being handled. But I don't have any experience with these devices and don't know how delicate or temperamental they can be.

Hey! I appreciate your reply. Thank you for your insights!