Rinnai RUC80i Training Program page 78

Troubleshooting Water Flow Issues:
•Cold water sandwich is when a tankless water heater is turned on, off, and
on again in a short period of time.
• Due to the 3-5 second activation time, this causes a cold slug of water to
travel down the hot water pipe.
•Crossover is when cold water is introduced into the hot
water line after downstream of the water heater.
• When this happens, it can "overtake" the flow from the
tankless water heater, thus causing the temperature at
the output to scale back.
• If strong enough, the crossover can cause the unit to
turn off altogether for a brief moment.
• Crossover can occur in single handled mixing valves,
washing machine connections, anywhere there is hot
and cold introduced at a single point.
•Pressure regulated and scald prevention fixtures can also cause intermittent flow issues.
•Clogged water filters, sink aerators, filtration systems, etc. can also cause flow issues.
• All of the above are common factors of tankless water heaters—understanding the basic technology
and various ways to alleviate such issues is important for consumer satisfaction
• Troubleshooting tip: If after isolating the appliance from the plumbing system and gpm flow and output
temperature are verified through the controller's diagnostic tests, the unit is likely performing to
manufacturer's specifications.
© 2016 Rinnai America Corporation
PROPRIETARY and CONFIDENTIAL
Enhancing Lives By Changing The Way Water Is Heated
78 5/4/2018