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Old 01-17-2018, 07:26 AM   #31
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Re: Plumbing Mystery?

at the older tank I can not rule out the water hammer arrestors
as I do not know how old they are,
do they predate this 2011 tank,
nor why they were originally installed... that said

I believe the sound you hear at newer tank is an echo
proven earlier by your closing valve at older tank did not stop noise
but that action did completely separate the 2 independent tanks

the fact that you do feel the noise best
in the cold piping at that tank indicates to me
very likely cause is that cold side heat trap nipple

the reason you heard noise without water use the other day
was that heater had evidently cycled on earlier as all tanks will...

I am reposting this statement made earlier for clarity:

If no pressure increase occurs during the heating cycle, & no pressure spikes occur in conjunction with noises; there is an open system (without backflow protection), your PRV is functioning properly & the noise is being produced by another source such as (but not limited to) a heat trap device at tank, defective water hammer arrestor, or a scald guard valve piston is somehow defective & chattering...

the following tests are more for elimination of where noise isn't
but in theory should help determine where you noise is coming from...
while not using any hot or cold water (for the duration of this test)
close both heater tank's isolation valves and leave them closed;
continue to keep both tank valves closed until directed to reopen
& definitely do not cycle open any hot water
(when preferably no one home to accidently open any faucet):

1st make note of usual temperature setting,
then turn up thermostat (only on new heater)
just until control cycles burner on; listen for noise...
wait until thermostat cycles back off &
turn thermostat back to original setting...

be sure you cycle newer tank before cycling older tank
did newer tank produce noise when heating?
& What about after heating stopped?
were noises occurring both during & after heat cycle?

now perform exact same test function to older tank -
turn up temp setting & listen for noise -
when thermostat cycles off, turn setting back down...
did older tank produce noise when heating?
& What about after heating stopped?
were noises occurring both during & after heat cycle?

If older tank is producing any noises, wait until those noises stop.
Immediately & quickly open the closed isolation valve for older tank
& listen for any more noises (due to thermal expansion you have created
by keeping heater valve closed during a heating cycle that prevented the expansion
from traveling back into cold piping thereby causing your cold side heat trap nipple to chatter)
pay attention as they may many or only a few more clicks.

After completing tests to older tank, return to newer tank.
if newer tank did not make any noises when cycling nor afterwards,
quickly open back that tank's isolation valve &
now listen for any noise coming from/at that tank
no noises from newer tank are your goal & the gold standard
you are listening for to eliminate this tank as culprit of your mystery.

If newer tank does not produce any noises
when isolated and cycled independently,
but your older tank does make noises
your mystery noises would have occurred whether
new tank was installed in 2017 or not IMO

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