Answer by John Canon for Would replacing my boiler's control board resolve intermittent issues after a water leak?

You may choose to clean the PCB if condensate has dripped onto it Even after water damage has evaporated, it leaves various salts and minerals on the circuit board, enough to affect operation.
Remove the PCB and place it on a folded towel. Use a 1-inch paint brush and isopropyl alcohol to lightly but thoroughly scrub both sides of the board. Don't let the iso enter the plastic relays. Use another towel to remove excess iso, then let it dry or blow clean air onto it. It's a standard repair for contaminated boards.