Perplexing Hot Water Problem


Last week we installed an electric tankless hot water system. Everything worked as expected for several days, so we know things were hooked up right. For the last couple of days there has been a strange hot water problem that no one can figure out. Here's what's happening: Hot water will only come out of the kitchen sink, but only if the bathtub is running full blast. Hot water will not come out of the kitchen sink if the tub is not running. The hot water to the kitchen sink does not cut out as long as the bath is running. Hot water will not come out of the tub valve or the valve in the bath sink at all now. Hot water will go into the clothes washer for a few seconds and then goes cold. IOW, the only hot water in the house goes to the kitchen sink, and then only when the tub is running. Other info: the bath valve is a single-control type. we tried replacing the mixing valve in the tub twice; no effect. we looked under the house to see if there is a hot water line leak, but there isn't. Does this make sense to anyone out there?
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e-mail sent. kenny b
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snipped-for-privacy@adelphia.net wrote in wrote:

Did you tell him exactly where the cross connection is? :-)
Eric
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Yep, I tried.
kenny b
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Sorry I should have posted here.
"After reading your post and assuming your installation is correct. It almost sounds as if you have a cross connection somewhere. I would have to see a layout of you water distribution system. Supplying water will of course take the path of least resistance, hence the cross connection of hot and cold. It may be the flow restriction through the unit, a bad valve or something else causing the water being routed through another route that has a shorter less restrictive passage. This usually occures when a bypass (valve) has been opened, or a mixing valve in line such as the washing machine is faulty. Any demand of hot water should bring a flow through the water heater, that would be the first thing to check. If hot water is being made it has to end up at the opened valve. When you state that under different flow conditions you have hot water, it points to the heater working but only under certain flow conditions. Lets not forget flow through the heater is what turns it on.
Good luck, let me know what you find. kenny b"
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The problem has been solved. There were two parts to the solution. Part one was that the tankless heater unit was defective and couldn't sense a low flow hot water request. That is why the tub had to be running full blast to get hot water from the kitchen sink. Part two of the problem was that when the contractor took the single-control valve off of the tub to replace the mixing valve, he put the handle back on in such a way that it couldn't turn far enough to activate the tub's hot water. Once the tub handle was remounted, then the tub worked fine. Thanks for all of your theories and suggestions.
cyd
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