A.O. Smith BTX-100/GDHE-50 – UIM Display Is Blank

On/Off is turned off
Water heater is not plugged in
Tripped Breaker – Blown Fuses
120 VAC power supply problems
24 VAC power supply problems
Defective transformer
Wiring or plug/socket connection problems
UIM communication cable problems

Important Service Reminder:
When performing any troubleshooting steps outlined in this service manual always consider the wiring and connectors between components. Perform a close visual inspection of all wiring and connectors to a given component before replacement.

Ensure wires were stripped before being crimped in a wire connector, ensure wires are crimped tightly in their connectors, ensure connection pins in sockets and plugs are not damaged or worn, ensure plugs and sockets are mating properly and providing good contact.

Failure to perform this critical step or failing to perform this step thoroughly often results in needless down time, unnecessary parts replacement, and customer dissatisfaction.

Ensure the on/off switch is on and working – replace switch if defective.
Check communication cable connections at UIM’s J2 Socket (page 27) and the CCB’s J16 Socket (page 36). Secure power and install a new comm cable. (standard Cat 5 network cable).
Closely inspect communication ports on CCB and UIM for damage or wear.
Ensure 120 VAC power is properly connected in the junction box on the back of the water heater.
Ensure 120 VAC is supplied to CCB’s J3 Socket pins 1 & 3. Hot wire to pin 1, neutral wire to pin 3 (page 36).
Check 120 VAC to transformer primary winding at CCB’s J1 socket pins 1 & 3 (page 36) with J1 plug removed, power on.
Check J1 plug and J1 socket on the CCB for wear or damage. Ensure plugs and sockets are mating properly and providing good contact.
Check for 24 VAC from transformer secondary winding at CCB’s J1 socket pins 4 & 5 with J1 plug inserted, power on. If 24 VAC is not present AND the two checks above were performed and the results were successful – replace the transformer. Check all wiring for shorts before powering up the new transformer.
Call the technical support phone number shown on the water heater labeling for further assistance if the problem has not been corrected after performing the procedures outlined here.

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