The key to high efficiency and long performance life for tankless water heaters is keeping the coils free of mineral buildup that occurs over time. One proven preventive maintenance solution in applications where the water is very hard is to use a soft-water generator ahead of the water heater.
When the tankless unit is installed, technicians should determine the baseline temperature increase — cold water in minus hot water out — by gauges installed on the inlet and outlet. Periodic checks of the temperature rise will indicate if the loss of heating capacity is significant. At that point, technicians should clean the unit.
Kits that include a bucket, pump, and hose are available to clean the inside of coils. To do this, technicians must shut off the gas and inlet water, and shut off the power at the fused switch for the unit. Next, they reduce system pressure by opening the valve at the overflow, put the portable sump pump into the 5-gallon bucket containing a recommended cleaner, and connect the pump outlet to the heater-water inlet with one of the hoses.
Then connect the other hose from the heater water outlet to the bucket to provide a recirculation path. Turn on the pump, and recirculate the cleaning solution for 45 minutes. The cleaning process should be complete, so technicians can reconnect and turn on the system and check the temperature rise again to measure the improvement. The system now should be at the base temperature rise.
The only other maintenance needed for tankless water heaters is a periodic check of water-pipe joints to find any leaks, a check of the gas line for leaks using a soap solution, and a cleaning of the electrical contacts to prevent overheating due to oxidation or pitting.
One advantage of electric coilless units is the elimination of scale buildup. These units also generally retain more than 95 percent efficiency throughout their performance lives.
Thomas A. Westerkamp is a maintenance and engineering management consultant and president of the work management division of Westerkamp Group LLC.
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