Perplexing Hot Water Problem

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cyd - 08 Jul 2008 17:04 GMT

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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kennybs@adelphia.net - 10 Jul 2008 07:19 GMT

> Last week we installed an electric tankless hot water system.
> Everything worked as expected for several days, so we know things were
[quoted text clipped - 16 lines]
> isn't.
> Does this make sense to anyone out there?

e-mail sent.
kenny b

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Eric G. - 11 Jul 2008 19:38 GMT

kennybs@adelphia.net wrote in news:5b840a27-7200-4c8a-893a-
ffc5b1d2a96d@d1g2000hsg.googlegroups.com:

>> Last week we installed an electric tankless hot water system.
>> Everything worked as expected for several days, so we know things were
[quoted text clipped - 19 lines]
> e-mail sent.
> kenny b

Did you tell him exactly where the cross connection is? :-)

Eric

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kennybs@adelphia.net - 12 Jul 2008 05:06 GMT

> kenn...@adelphia.net wrote in news:5b840a27-7200-4c8a-893a-
> ffc5b1d2a...@d1g2000hsg.googlegroups.com:
[quoted text clipped - 24 lines]
>
> Did you tell him exactly where the cross connection is? :-)

Yep, I tried.

kenny b

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kennybs@adelphia.net - 12 Jul 2008 05:14 GMT

> > > e-mail sent.
> > > kenny b
[quoted text clipped - 4 lines]
>
> kenny b-

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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cyd - 25 Jul 2008 18:08 GMT

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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Homeowner Forum / Plumbing / July 2008

Perplexing Hot Water Problem