On Jul 8, 11:58 am, cyd wrote:
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?

When you say "hot water will not come out of ...", do you mean that
water comes out, but it is not hot -- or do you mean that no water at
all comes out?