I have a tankless with a descaler on the cold water input. When I turn on the hot water at the faucet it takes a minute or so to get hot water. Then I'll hear some banging/knocking of the pipes.
However, if I leave the hot water running, it turns to cold water.
What could be happening?
update It is a Noritz NR981-OD-NG. Natural gas model. We just installed the unit a few weeks ago. I just started to use it this past week.
This is our only hot water heater and is rated for 2 to 3 showers.
The hot water is on full and the cold water is off.
update 12/29/16 Could the flow of water be causing the hot water heater to not activating to heat the water? I can hear the hot water heater 'working' even when cold water is coming out of hot water faucet. From the specs of the water heater: "Minimum Activation Flow Rate 0.5" How can I tell/measure what the flow rate is ???
update 1/3/2017 Resolved! The plumber and I changed out the water limiting spout cover and that did the trick. Our local gas company gave us a water savings kit and we used the water limiting spout (rated for 1.5 gpm) and that seemed to fix the problem.