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
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
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
Does this make sense to anyone out there?
Sorry I should have posted here.
"After reading your post and assuming your installation is correct.
almost sounds as if you have a cross connection somewhere. I would
see a layout of you water distribution system. Supplying water will
course take the path of least resistance, hence the cross connection
and cold. It may be the flow restriction through the unit, a bad valve
something else causing the water being routed through another route
a shorter less restrictive passage. This usually occures when a
(valve) has been opened, or a mixing valve in line such as the
machine is faulty.
Any demand of hot water should bring a flow through the water heater,
would be the first thing to check. If hot water is being made it has
up at the opened valve. When you state that under different flow
you have hot water, it points to the heater working but only under
flow conditions. Lets not forget flow through the heater is what turns
Good luck, let me know what you find.
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.
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