GE GEH Series Service Manual page 27

Three Heat Sources
The water heater has 3 heat sources:
1. Upper heating element
2. Lower heating element
3. Condenser
Only ONE heating source can be on
at a time.
The upper heating element has
priority. If a large temperature
increase is required, the upper
element is used (except in eHeat).
The lower element and condenser
are both considered "lower" heat
sources.
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