Rinnai ByPass Servo Troubleshooting Manual page 16

9. Check system operation to see if the water heater is continuously short cycling. If so, heat from
short cycling can transfer into the copper heat exchange and trip the bi-metal switch.
Investigate to see what is causing the short cycling such as aqua-stats with a low delta T.
Increase set point of aqua-stat by at least twenty degrees lower than the water heater's set
point. This will normally stop the unit from short cycling.
WARNING: Turn off the electrical, gas and water supply to the water heater before proceeding.
10. Inspect burner manifold, burner assembly and heat exchanger copper fins for debris build-up or
blockage. If you find debris build-up inside the heat exchanger that has led to a code 14, replace
the heat exchanger.
11. Inspect the front, sides and back of the heat exchanger surface for cracks, separations,
discoloration or damage of any kind. If you find any of the above mentioned items replace the
heat exchanger.
12. Inspect all components inside the water heater cabinet for signs of excessive heat damage. Take
note of the copper surface of the heater exchange where the combustion box and copper meet
for discoloration. If discoloration (black) surface is noted replace heat exchange. This indicates a
blockage or debris build up between the copper fins inside the heat exchange.
13. Verify venting is within vent clearance specifications and lengths per manufactures'
recommendation.
14. If code 14 still appears after performing the above inspections, replace PC board.
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