We have a tankless water heater (Aquastar at least 10 years old). I had to have a plumber install flush valves last year, because it had none and I didn't realize it had to be cleaned with vinegar. We have cleaned it with vinegar. I have also let the vinegar heat up to ensure the unit is working and the vinegar gets VERY hot. However, when we run water it does NOT. The water at faucets is about 76-78 degrees. Showers are even worse. If I turn on the sink AND shower I can warm it up enough to tolerate it! If I turn off the hot water to the house, the faucets in the kitchen and bathroom sinks will go off (when hot water only is turned on). In the showers, there is a trickle of water in both the cold and hot positions when the hot water is turned off to the house. Is there just a bleed over causing this? Would a bleed over in the showers cause the problems at the sinks too? Thanks for any help!

Troy

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If I turn off the hot water to the house, the faucets in the kitchen and bathroom sinks will go off (when hot water only is turned on).

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This statement makes no sense, but it really doesn't matter as we can't really help with a problem like this. Here, these tankless water heaters are notoriously finicky and we could spend tons and tons of time troubleshooting back and forth and still not arrive at the problem.

In this case, you should probably call the plumber back and have him fix the VOLUME/FLOW issue...;)

Good luck!

Mark