I had a new hot water heater installed, and shortly after that, it
would discharge water. The plumber who installed it, said that the
pressure was too high likely in the house. He looked at the pressure
reducer value which he said was old and broken. So he replaced it. He
also claimed this would stop the water spike we got in the house. I'm
defining a water spike, that at random times during the day or night,
when you turn on any facet water will blast out for about 10 seconds
and then return to a normal flow. I have not been able to see a pattern
for this. I have seen it do this within minutes after using the shower
and then getting a drink a water from the kitchen sink.
The plumber, who by the way has a master plumber's licenses was
surprised that we still had the water spike problem. Assuming that the
new unit might be defective, he replaced it with one that was assemble
in the US instead of China, thinking that perhaps the charge in product
might have caused the problem.
This didn't solved the problem, still several times a day, without
warning water comes blasting out. The plumber said he didn't know what
to do, since he didn't think it was likely that both of these pressure
reducer valves were defective. I asked if perhaps the ones he was
installing simply were robust enough to handle the high pressure and he
said that this is a very normal device he has been installing in my
area for many years and never had a problem.
This led us to talk with the local water company. Maybe the pressure
coming in from the street was so great that this device couldn't handle
it when it would spike. After many phone calls I finally got the water
company to return my call and be interested in the problem. The last
call, I gave him the phone number of my plumber since he was most
familiar and understood the system. After all, I'm just a home owner
and don't know much about this stuff. I got a phone call back from the
water company and said he talked with my plumber and after discussing
the problem the plumber agreed with the water company that we should
install an expansion tank over the hot water heater. I explained that
the water spikes come from the hot water and the cold water as well.
How is an expansion tank over the hot water heater going to solve the
cold water spikes too I guess, and he said he didn't know. He said the
plumber will be contacting me.
I talked to the plumber and he said that about in 25% of the homes that
they install new hot water heaters, they need expansion tanks, and that
this affects the hot and cold water as well. While I am waiting for a
quote to have this expansion tank installed, I thought I would post and
ask if others have had this experience or could shed some light on it.
Does an expansion tank sound like the solution?
Revoke his license.
A thermal expansion tank is required any time a PRV is
present on a municipal supply.
Yes, he can get away without one in 75% of the installs
maybe because the street pressure is low enough.
The exp tank gets connected on the *Cold* inlet
side of the heater. When the water heats up, it
expands, raising the pressure in the tank.
The PRV prevents the expansion from backing up
out to the street. (There are exceptions to this,
but not important here.) To absorb these spikes,
an expansion tank is necessary.
So, the pressure spikes you see do affect *both*
Hot and Cold lines since they are joined by the heater.
Retail on the exp tank is about $40 to $50.
Install is easy.
Yes, with the PRV installed you need an expansion tank.
I'd also recommend a check valve on the cold water inlet of the water heater
to eliminate the cold system as part of the expansion area and to ensure
there's no backflow from the heater into the cold system.
"I'd also recommend a check valve on the cold water inlet of the water
heater to eliminate the cold system as part of the expansion area and
ensure there's no backflow from the heater into the cold system. "
1. The money would be better well spent on beer and pizza.
2. Some PRV's allow for thermal expansion, eg. Watts AUB series.
3. The thing you need to get is a new plumber, Maybe one that owns a
What I would guess is: The dynamics of the reducing valve maybe too slow in
getting to its steady state regulating position. With no flow the valve is
in a closed position. When there is a sudden flow demand (opening a faucet)
the valve moves opens to provide flow but actually overshoots its steady
state position. For whatever reason it then slowly closes down to regulate
the pressure. It's during that time frame that there is high flow out of the
faucet. In high performance systems, PRV are fast acting with time
constants in the order of 15-20 millisecond. There are many things that
slow down the transient response of these type of valves--in many cases it
is getting the control pressure to bleed down allowing the valve to respond
quickly Usually a damping orifice being too small is one reason.
Just what people need here is more phyco babble bullshit to confuse
people even more. When all that was really needed was a plumber with a
gauge and a little knowledge on how to use one.
Instead you got a plumber that replaces things because they look old so
it must be bad theory.
Your response is very refreshing--be so good as to explain just how a gage
will resolve the problem. What does the pressure tell you if it's high? or
if it's low? Or if it goes from high to low? What it does after or when a
faucet is opened? In fact, if it's not bled properly you can't believe
anything it tells you other than steady state. In many cases you have to
understand the problem before you can fix it. Oh, BTW, sorry if you got
confused--but when you have an IQ about the same as your hat size that's
easy to understand.
errr ... I thought it was quite nice to get some intelligent engineering
comment on the issue actually - what a shame a little simple physics seems
to have been confused with 'phyco babble bullshit' ...
I agree the guy's plumber sounds flaky ...
The public water system pressure in my area is always changing up and down
several PSI day and night. I installed an new water heater a couple of years
ago and found that an Xtrol type expansion tank for potable water was
necessary to keep the water heater's pressure relief valve from popping
every so often. I had tried another relief valve first, but the tank was
necessary to absorb the pressure spikes.
"Funny" thing is my water meter (in my basement) can be observed oscillating
forwards and reverse if you look at the spinner dial on it top while you
hear the meters chamber measuring the volume flow while this is happening.
What is NOT so funny is that the actual dials on the meter seem not to go
backwards (the 1/10 cu ft dial) when the spinner is in reverse. I don't
think it adds up to any real dollar amount to my bill. But the frequent
meter noise is annoying.
Funny how this thread came up as I was considering installing a check valve
in the cold water feed to my hot water tank!
I will put one in for sure now.
Bob (another Bob)
here's an answer to much of the pressure speculation:
this one has a hose female connector:
300 PSI WATER PRESSURE TEST GAUGE
300 PSI Water Pressure Test Gauge
THDS Part #: 153000
this has a 1/4" MIP [male iron pipe thread] connector
100 PSI WATER PRESSURE TEST GAUGE
100 PSI Water Pressure Test Gauge
THDS Part #: 153050
"I had a new hot water heater installed, and shortly after that, it
would discharge water."
3) faulty T&P
How are you going to tell if the discharge is either a faulty T&P or
due to pressure, you can't without a gauge.
How are you going to tell if the pressure is from a bad PRV, you can't
without a gauge.
You can watch the spikes on a gauge and even verify thermal expansion
is happening with a gauge.
Only an idiot would come to a conclusion without facts, at the expense
of a homeowner.
Good questions, but a very feeble example. First of all, most home systems
don't have a point of entry where a pressure gage can be installed. Where
would you put one without taking anything apart? Obviously, one can rule
out temperature very quickly--not hard to measure or just shut off the water
heater and see if the problem recurs. Then there are times when it is just
as efficient and cost effective to substitute as it is to try and
troubleshoot. In this case, the T&P first since it is the easiest to remove
and it is also the least expensive. Maybe you can watch spikes on a gage but
in no way are you seeing what's actually happening. Have you ever recorded
large amplitude, high frequency pressure pulses with and without a gage
installed in the system? I have!! First of all, a gage does not have the
capability to respond to a transient pressure pulse; it tends to act as an
accumulator. The net result is that it attenuates and dampens out pressure
pulses in a system. Finally, you didn't address the prime topic of
discussion which is why there is a high flow for approx 10 sec after opening
a faucet. Just use some common troubleshooting sense------- If you have a
normally functioning PRV how can a defective T&P valve cause high flow out
of a faucet for 10 secs? Flow is a function of Supply Pressure and system r
esistance. The only component that is responding to the city supply pressure
is the PRV. It has to reduce that pressure to it's set point (household
pressure) and keep it at that value independent of the flow demand. The
slower the PRV responds, the bigger the variation in household pressure and
the more the variation of flow out of the faucet. In this case a gage would
certainly show a gradual reduction of pressure over a period of 10 secs
pointing to the PRV.
Laundry tray, hose bibb, washing maching valve, the water heater drain
A plumber would know this.
> Obviously, one can rule out temperature very quickly--not hard to
measure or just shut off the water heater and see if the problem
Thats why it was listed but I responded with pressure.
Really, Most professional plumbers not only want to know but need to
know what is causing the problem before repairs are made. Someone's
paying you for a professional opinion and your guessing. I guess you
just defined your self.
As far as the rest, I won't waste my time. A real plumber would have
had the problem solved and repaired on the first trip at a fair price.
Hey thats why we get paid the big bucks, right.
You can see the real plumbers here responded with thermal expansion, a
gauge would prove that in seconds if the system was closed. The gauge
would also prove the PRV was working.The thermal expansion causes the
spike in pressure equally throughout the system as long as the PRV is
working and is closing the system.
We're not building a watch here, this is basic plumbing.
Yes an expansion tank is probably needed to solve the problem, but that
should of been confirmed from the begining. Instead his plumber
followed your play book and changed the PRV twice.
In this case, the T&P first since it is the easiest to remove
Once again you responded by sticking to the simple easy solution of an easy
problem and completely ignored and tip toed away from the initial question
(and my questions) that started this whole discussion. First, to address
your comments: You must be a very unusual plumber--I don't ever recall one
that actually measured anything--typically, they replaced or cleaned out,
nothing scientific or mind boggling.
Thermal expansion: Your comment:*** "The thermal expansion causes the
spike in pressure equally throughout the system as long as the PRV is
working and is closing the system.***
Dribble, and it surely indicates that you really don't understand what
you're talking about. Think of thermal expansion as it applies to the
cooling system in your car. As the coolant temp increases, volume increases,
pressure increases until it gets to the radiator cap setting and then the
coolant spills over to the expansion tank. No spikes in pressure--- it
increases along with the temperature. With the PRV and all faucets closed
you have a volume of water trapped between them--aka, a hydraulic lock. As
the temp is increased, up goes the pressure-what do you think would happen
to your piping if there was no escape route via a relief valve built in to
the PRV or the water heater T&P valve? No different than if the water
froze--something is going to break! Obviously, an expansion tank provides
the room to accept the volume increase--that's why it is recommended. Not
rocket science. Now once again--would you just stick to the subject--Why do
you think there is a flow of water that lasts for approx 10 seconds when the
faucet is opened? What do you do to resolve it?
Oh yes--you guys do make BIG bucks and in many cases it's justified. One
should get paid not only for the actual work but for what he knows. But do
you really know what BIG bucks are? Think of the most expensive thing you
ever worked on or charged. I worked on a product that sells for 2.5 million
dollars. At times I've had to make a judgment call on resolving a problem
and replaced a component(s) worth about $50,000 a piece. Early on in the
development process (and the need to resolve a problem) required the use of
a facility that, with a discount, cost $10,000 an hour with a 10 hr.
minimum. Do the arithmetic, it cost $100,000 a day, sometimes for 2-3
months at a time. Finally, our product ended up as a key component of a
$32,000,000 machine. In the troubleshooting process there is a difference
between shot gunning and selective replacement of components. At times,
the least likely of two components might be replaced first because it might
only take 1 hour vs. 8 hrs. for the most probable one. Better to waste an
hour than maybe 8 hours. Sorry if I got carried away--didn't mean to.
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