Plumbers replaced the temperature control module. The metal housing was cracked. The most common problem with this particular module is that the component which connects to the tank is plastic and it usually breaks/cracks/splits. The plumber informed me that the one they removed had a metal cap on it so Honeywell has apparently attempted to remedy the common problem.
Backside (hot water heater side) of module showing plastic component with metal cap:
Front side (with control panel removed):
Front side (with control panel removed) bottom view: