1 utility pump (Typically, this type of utility pump is self-priming.)
3 hoses (Typically the utility pump comes with 1 hose. Additionally, washing machine hoses work well for this operation.)
2 buckets (one or five gallon)
2 gallons (+/-) white vinegar
SET-UP:
Attach one hose from the hot outlet service port of the tankless water heater to one of the buckets. Attach one hose from the inlet of the pump to another bucket. Attach one hose from the pump to the cold water inlet service port of the tankless water heater.
HOW IT WORKS:
The flow from the first bucket filled with fresh vinegar goes into the pump. The pump sends the vinegar into the water heater via the cold water service port and then out the hot water outlet port into the second bucket.
PROCEDURE:
Simply open the service port valves and turn on the pump. The vinegar will begin to flow through the tankless heater and come out of the hot side outlet service port into the return waste bucket.
WHAT PERIOD OF TIME IS NECESSARY:
Due to many variables, the time that this cleaning procedure will take is not something that can be predicted. Depending upon the preparedness and abilities of the person doing the work, the hardness of the water, if there is a softener in use, and how long it has been since the last cleaning, it may take as little as 45 minutes or as long as a couple of hours. Repeat this procedure as many times as necessary until the vinegar runs clean into the return bucket.
During this operation, you may choose to let some vinegar sit in the heater for a few minutes. Do this by isolating the vinegar by turning off the port valves. First close the outlet hot side port service valve, followed by the cold side port service valve. Then immediately turn off the pump.
Then, in a few minutes re-open the service valves, re-start the pump and see if this may have loosened any additional scale.
Finally, do the same procedure with fresh water to flush all remaining vinegar from the tankless heater. Do this until you have run about five buckets of clean water through the heater.
DISPOSAL OF REMAINING SOLUTION:
Vinegar is not harmful and even the most environmentally conscious person can simply pour this solution down the household drain.