CAUTION: For your safety, DO NOT attempt repair of electrical wiring, controls, heating elements, or other safety devices. Refer repairs to qualified service personnel.
Possible Cause: Water temperature may be set too low.
What To Do: See the Water Temperature Adjustment and Water Heater section.
Possible Cause: Hot water usage pattern exceeds the capability of the water heater in current mode.
What To Do: Wait for the water heater to recover.
Possible Cause: Cold water inlet temperature may be colder during the winter months.
What To Do: This is normal. The colder inlet water takes longer to heat. Consider increasing the set temperature as described in the Water Temperature Adjustment section.
Possible Cause: Leaking or open hot water faucets.
What To Do: Make sure all faucets are closed.
Possible Cause: Long runs of exposed pipe, or hot water piping on outside wall.
What To Do: Insulate piping.
Possible Cause: Water Connections to unit reversed.
What To Do: Correct piping connections.
Possible Cause: Recirculating System Interference (if installed).
What To Do: Check flow rate is not set too high. Insulate piping.
Possible Cause: Installation is not south facing with minimized shading.
What To Do: Correct installation to face south and minimize shading.
This answer is applicable for the following models: GT50C10BAM, GT40C10BAM, GT25C10BAM.