Codes for Tankless Water Heater!

Village Plumbing was able to schedule yesterdays estimate for today service call. We went to Malibu dug up area were we need to make connections. Also Village Plumbing and Heating was in Los Angeles, giving another estimate on installing a toilet. In Tarzana, we had a call for a tankless water heater, customer had a TM1 code 66. Checked and found bypass leaking. Removed and replaced, tested working fine. Heater does not have water treatment on heater. We recommend that the tankless water heaters have some kind of water softener and or treatment system on there unit.