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Default Water heater relief valve -- POW!

Oh, boy, do I feel dumb. But hopefully someone will learn
something from my embarrassment that will help to keep
them safe.

We have a gas-fired water heater here. It has been our
practice for a while now to cut the thermostat on that to
minima if we are leaving the house for more than a day
at a time. Why pay and waste energy to heat and re-heat
water which no one will use?

On returning, I turn the t-stat back up to a level which
provides comfortably hot water. There isn't any degree
rating on the rotary knob, so I have figured out empirically
what the "hot enough" point is.

It never, ever would have occurred to me that I should install
some sort of a physical guard to prevent knob travel beyond
that point. And I could have absolutely bloody well sworn that
I had shown my wife what the set point was supposed to be.

Apparently not. We came home today from holiday travels,
and I went to wash my hands and said, "Ah, it's cold, the
water thermostat should be adjusted back up."

She was in the garage and said, "I'll get it!"

I was roadburnt, and didn't pay any attention to the possible
ramifications of having someone else do a job which I normally
would do.

A few hours later (during which there was lots of hot water use
for baths and whatnot) we were relaxing in the back of the house.
Suddenly, we looked at one another. "Did you hear that?" "Yep.
But no idea what it might be."

Reconnoitering the front room and kitchen, nothing. She looked
into the garage and said, "Ack! The water heater has exploded!"

I ran out and saw nothing of the kind (fortunately). What I did
see was a pressure relief pipe (which in this case discharges
straight onto the concrete floor) spewing steaming water.

Glanced at the rotary knob on the water heater thermostat. It
was ALL of the way over. Probably thirty angular degrees of travel
past the "hot enough" point. If there had been someone with the
wit to inscribe a burner setting from 1 to 10 on the rotary
surround, this setting would have been 11. Utterly maxed out.

Touched the pressure relief pipe just below the PR valve. Nearly
burned my finger on it.

Oh feathers. Cut the thermostat to zero. Turned on the utility
sink hot tap. Incredibly scaldingly hot water came out and kept
on coming out, in a huge cloud of steam. Sent the wife to run
other taps on full.

I should have had the presence of mind to go valve off the cold
water inflow, but there is no way to do that next to the heater --
that action requires a trip outside to shut off the master, and I
had my hands full dealing with lots of suddenly very wet stuff
which we had stored in the garage.

After a couple of minutes, the steam coming from the discharged
water was greatly lessened, and the pressure relief pipe felt much
cooler when touched, though still flowing visibly. I tripped the lever
on the relief valve and that reset it. Flow stopped. Crisis over.

The unit has now cooled down to garage ambient temperature,
and I am not going to turn it back up until we have carefully
thought through the return-to-service process.

Okay, lessons learnt up to this point:

(a) Always, ALWAYS document on the device what the proper
normal setting should be;

(b) Strongly consider mechanically excluding settings above
"normal" -- even settings which would not have blown the
relief would have been easily hot enough to scald at the tap;

(c) Take the time to arrange graceful failure modes even for
seldom activated systems -- routing the pressure relief pipe
to an exit hose had occurred to me before, but I had never
made it an action item;

(d) Brief people on how to set controls if they're not yet so
informed -- and people who find themselves unsure should
take time to ask;

(e) Be sure to test safety systems on a regular schedule --
I shudder to think what would have happened if that relief
valve had not tripped when it did. I have flipped the test lever
in the past when I thought of it, but will be formally rigorous
about it in future.

That's what I have learned. Here's what I am yet to learn,
and about which hopefully someone will be able to inform me:

(f) Of what gotchas should I be aware when attempting to
return the unit to service?

(g) What are the odds that the heater has been damaged
by the overheat/overpressure event? The relief valve tag
specifies release at 150psi/210F, which is pretty impressive.
What's more, this unit has a build tag dated 1985! Assuming
that it was installed at that time (it may be old stock) that is
impressive longevity. My experience has been that modern
water heaters seldom last more than a decade even without
adverse events of this type. And while I would have liked to
eke out another few years, if the heater is likely to have been
compromised, I don't want to risk having it split wide open
a few months later on.

(h) Even if the tank and heater assembly seem OK, should
I think about replacing the relief valve itself? It was fine before
this, with no drips or hisses. I do want to be quite sure that
the relief will open when it needs to, though. Note that there
is also an unknown in that a new-in-box valve might itself
be junk -- the current valve at least has been demonstrated
to work properly under field conditions.

Comments and feedback actively solicited. I'd prefer to see
them here in the newsgroup rather than mailed to me: this
in-box is utterly soaked with spam.

And before I close, let me take this opportunity to wish the
top of the season to you all!

C

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Toller
 
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Default Water heater relief valve -- POW!


(g) What are the odds that the heater has been damaged
by the overheat/overpressure event? The relief valve tag
specifies release at 150psi/210F, which is pretty impressive.
What's more, this unit has a build tag dated 1985! Assuming
that it was installed at that time (it may be old stock) that is
impressive longevity. My experience has been that modern
water heaters seldom last more than a decade even without
adverse events of this type. And while I would have liked to
eke out another few years, if the heater is likely to have been
compromised, I don't want to risk having it split wide open
a few months later on.


It shouldn't have been damaged; hopefully you won't get the
pressure/temperature up that high again.
Personally I would not want a 20 year old heater in my house. I have a 25
year old heater in my cottage, but a leak won't do anything horrible there.

(h) Even if the tank and heater assembly seem OK, should
I think about replacing the relief valve itself? It was fine before
this, with no drips or hisses. I do want to be quite sure that
the relief will open when it needs to, though. Note that there
is also an unknown in that a new-in-box valve might itself
be junk -- the current valve at least has been demonstrated
to work properly under field conditions.

A 20 year old valve is a little spooky also. Did you test it regularly? If
not, you are darn lucky it worked! Again, I would replace the whole tank.
Comments and feedback actively solicited. I'd prefer to see
them here in the newsgroup rather than mailed to me: this
in-box is utterly soaked with spam.

I wonder if it went because of temperature or pressure. You would think
they design them so that the highest setting isn't too high, but perhaps
your thermostat is off also. Another good reason to get rid of it.
Do you have a closed system without an expansion tank. If so, it was bound
to happen eventually.

I have tested my system by letting it cool down, and then setting it to the
highest temperature, while monitoring the pressure. It doesn't exceed the
street pressure (90psi) so I know the relieve valve on my pressure reducer
is working. Probably should test it again, or at least clean it like the
instructions say.... (or bite the bullet and put in an expansion tank)

And before I close, let me take this opportunity to wish the
top of the season to you all!

You too. Be thankful the valve worked!


  #4   Report Post  
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buffalobill
 
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Default Water heater relief valve -- POW!

"Temperature/pressure relief valve (T&P)
This valve is designed to prevent a tank from exploding if temperature
or pressure exceeds safe limits, by opening and venting. Unfortunately,
residential valves are somewhat prone to failure. They should be
checked once a year by pulling up on the handle. Water should flow
freely out and stop when you let go of the handle. If it does nothing,
runs or drips, then the valve should be replaced. Banging on the handle
with something hard, like pliers, sometimes will stop drips or even
runs. If not, replace the valve. Hooking up the drain line with a union
or flex connector makes T&P replacement MUCH easier.

People don't like to test their T&Ps. But then, we don't think it's so
much fun to wake up in the hospital, or to patch a big hole in the
roof, either. When water heaters explode, it's catastrophic. People are
injured or die; buildings are severely damaged. Test your T&Ps! And one
more thing: T&P drain lines should go down and out. Never up. If the
valve opens, water will pool there and corrode it shut. Or freeze in
the line in colder climes. We've seen lines plumbed uphill so many
times we've lost count. But there SHOULD be a drain line, usually to
within about six inches of the floor, or plumbed outside. That's code
around here. It's to prevent you from being scalded if the valve should
open while you're standing next to it.

Finally, if water is running out of your T&P line, look for the cause.
It might just be a bad T&P. But it could also signal high-pressure
problems or a dangerously defective control. Don't ignore it!"

this information and more at:

http://www.waterheaterrescue.com/pag...er-safety.html

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Red Neckerson
 
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Default Water heater relief valve -- POW!


wrote

Oh, boy, do I feel dumb. But hopefully someone will learn
something from my embarrassment that will help to keep
them safe.

We have a gas-fired water heater here. It has been our
practice for a while now to cut the thermostat on that to
minima if we are leaving the house for more than a day
at a time. Why pay and waste energy to heat and re-heat
water which no one will use?


SNIP

Next time just turn the breaker off......




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Bob
 
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Default Water heater relief valve -- POW!

He probably doesn't have a breaker.

"Red Neckerson" wrote in message
newsZ8sf.4171$X86.3228@trnddc04...

wrote

Oh, boy, do I feel dumb. But hopefully someone will learn
something from my embarrassment that will help to keep
them safe.

We have a gas-fired water heater here. It has been our
practice for a while now to cut the thermostat on that to
minima if we are leaving the house for more than a day
at a time. Why pay and waste energy to heat and re-heat
water which no one will use?


SNIP

Next time just turn the breaker off......




  #7   Report Post  
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Mikepier
 
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Default Water heater relief valve -- POW!

Similiar story that happened to me. I was working in a 6 family apt
building. One of the apt's had a bathtub faucet that was leaking hot
water bad. I did not have the right parts with me. So I shut off the
bathroom hot water feed in the apt and I told the tenant " I'll be back
tomorrow with the parts."
Well the next day I came back and I found water in the basement.
Apparantly some tenant thought the water was not hot enough ( probably
because of the bad leak) and took it upon himself to raise the T-stat.
And because I stopped the leak the day before by shutting off the main
bathroom feed, the hot water heater built up in temp and pressure and
let out water in the relief valve. So I had to replace the relief valve
as well.

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Berkshire Bill
 
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Default Water heater relief valve -- POW!


"Red Neckerson" wrote in message
newsZ8sf.4171$X86.3228@trnddc04...

wrote

Oh, boy, do I feel dumb. But hopefully someone will learn
something from my embarrassment that will help to keep
them safe.

We have a gas-fired water heater here. It has been our
practice for a while now to cut the thermostat on that to
minima if we are leaving the house for more than a day
at a time. Why pay and waste energy to heat and re-heat
water which no one will use?


SNIP

Next time just turn the breaker off......


Did you notice he's talking about a GAS water heater ?

Happy modeming,
Bill K.


  #9   Report Post  
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Default Water heater relief valve -- POW!

I second the comment about not having a 20 year old gas water heater.
That is way beyond the typical life expectancy of 10-13 years. If it
were mine, I would replace it right now.

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Stretch
 
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Default Water heater relief valve -- POW!

Probably the relief valve tripped on temperature, just what it was
supposed to do. With the relief valve that old, yes I would replace
it. The water heater should be fine. If it ever leaks, the water will
only wet the garage floor. If it were in the house, or where the water
could damage the structure, I would want an emergency pan under it
piped to the outside.

DO NOT put a hose on the relief valve discharge pipe, that would
restrict flow. It should be piped to the outside with an elbow turned
down. The relief valve discharge discharge should be piped FULL SIZE,
with no more than 25 feet of length and no more than 4 elbows in the
length (Old code but a good idea). If the relief valve discharges on
the floor, the pipe should terminate no more than 6" above the floor to
reduce spalshing.

Stretch



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Default Water heater relief valve -- POW!

On 26 Dec 2005 21:34:22 -0800, wrote:

(e) Be sure to test safety systems on a regular schedule --
I shudder to think what would have happened if that relief
valve had not tripped when it did. I have flipped the test lever
in the past when I thought of it, but will be formally rigorous
about it in future.


See this explosion:

http://www.waterheaterblast.com/index.html

Oren
"My doctor says I have a malformed public-duty gland
and a natural deficiency in moral fiber, and that I am therefore
excused from saving Universes."
  #12   Report Post  
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Tom Horne, Electrician
 
Posts: n/a
Default Water heater relief valve -- POW!

Red Neckerson wrote:
wrote


Oh, boy, do I feel dumb. But hopefully someone will learn
something from my embarrassment that will help to keep
them safe.

We have a gas-fired water heater here. It has been our
practice for a while now to cut the thermostat on that to
minima if we are leaving the house for more than a day
at a time. Why pay and waste energy to heat and re-heat
water which no one will use?



SNIP

Next time just turn the breaker off......



Just for the sake of our eduction would you mind telling us where he
would find a breaker that would affect the functioning of a "gas-fired
water heater"? Unless the unit is a high efficiency type that uses
blowers for exhaust and combustion air there is no breaker for a
"gas-fired water heater".
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
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Bob
 
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Default Water heater relief valve -- POW!


"Toller" wrote in message ...
I have tested my system by letting it cool down, and then setting it to the
highest temperature, while monitoring the pressure. It doesn't exceed the
street pressure (90psi) so I know the relieve valve on my pressure reducer
is working. Probably should test it again, or at least clean it like the
instructions say.... (or bite the bullet and put in an expansion tank)


You actually know nothing of the sort. If the pressure doesn't go above the
street pressure, you know that there is no anti-backflow valve where the
water comes into your house. If the relief valve was limiting the pressure,
water would be coming out the relief valve outlet.

Bob

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Toller
 
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Default Water heater relief valve -- POW!


"Bob" wrote in message
...

"Toller" wrote in message
...
I have tested my system by letting it cool down, and then setting it to
the
highest temperature, while monitoring the pressure. It doesn't exceed
the
street pressure (90psi) so I know the relieve valve on my pressure
reducer
is working. Probably should test it again, or at least clean it like the
instructions say.... (or bite the bullet and put in an expansion tank)


You actually know nothing of the sort. If the pressure doesn't go above
the
street pressure, you know that there is no anti-backflow valve where the
water comes into your house. If the relief valve was limiting the
pressure,
water would be coming out the relief valve outlet.

Sure I do. The prv acts as a anti-backflow valve UNTIL the pressure in the
house exceeds the street pressure. Then the relief valve allows backflow.

Actually I was confused about what I said, since I did this two years ago.
The pressure never got above 85psi and the street is 90psi, so the relief
valve never got tested. Sorry.


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Default Water heater relief valve -- POW!

Generally, the one component you might replace is the "zinc"- the
protective anode rod; likely way beyond time for that.

I'd prepare to replace heater in the next year or so- monitor it for
any leaks or odd behavior. Pretty simple process, especially if you
have all the fittings an tools you might need ready. Newer units have
additional safety devices, and are capable of higher efficiency than
yours.

You NEVER want a careless person twiddling around with something like
that t-stat; sorry, but your wife qualifies. At the very least, someone
could have gotten very badly burned- boy, are you lucky!

What I find much simpler is to leave the t-stat alone, and turn the
control from "pilot-only" to "on" or vice-versa. But then, mine is not
in garage, so there's no threat of freezing.

J



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Default Water heater relief valve -- POW!


wrote:
Oh, boy, do I feel dumb. But hopefully someone will learn
something from my embarrassment that will help to keep
them safe.

It never, ever would have occurred to me that I should install
some sort of a physical guard to prevent knob travel beyond
that point. And I could have absolutely bloody well sworn that
I had shown my wife what the set point was supposed to be.


I've thought about a mechanical stop that would prevent this.

I ran out and saw nothing of the kind (fortunately). What I did
see was a pressure relief pipe (which in this case discharges
straight onto the concrete floor) spewing steaming water.


Yes an actual explosion could easily leveled the garage!

......
After a couple of minutes, the steam coming from the discharged
water was greatly lessened, and the pressure relief pipe felt much
cooler when touched, though still flowing visibly. I tripped the lever
on the relief valve and that reset it. Flow stopped. Crisis over.


Well it seemed like the pressure relief valve did it's job! Usually
that overflow is routed to a drain if one is available.
An interesting thing is to Google "water heater explosions" and Watts,
who invented the T&P valve. I have seen shows about how steam
locomotive boilers have exploded and also pictures of heating boilers
and water heater explosions. Sometimes they'd find the exploded heater
blocks away. Imagine a 75 gallon superheated steam rocket!
Also one site recommended replacing that valve every three years! but
then they were made them.
So all in all you actually had a good holiday.
Richard

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Rich Greenberg
 
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Default Water heater relief valve -- POW!

In article om,
wrote:
Oh, boy, do I feel dumb. But hopefully someone will learn
something from my embarrassment that will help to keep
them safe.

We have a gas-fired water heater here. It has been our
practice for a while now to cut the thermostat on that to
minima if we are leaving the house for more than a day
at a time. Why pay and waste energy to heat and re-heat
water which no one will use?


What I would suggest is rather than twist the thermostat, switch the gas
valve to pilot or off. Pilot if there is any danger of freezing or
humidity is high, off otherwise.

If its constructed so that lighting the pilot is a royal pain, forget
off and just turn to pilot.

--
Rich Greenberg Marietta, GA, USA richgr atsign panix.com + 1 770 321 6507
Eastern time. N6LRT I speak for myself & my dogs only. VM'er since CP-67
Canines:Val, Red & Shasta (RIP),Red, husky Owner:Chinook-L
Atlanta Siberian Husky Rescue. www.panix.com/~richgr/ Asst Owner:Sibernet-L
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George E. Cawthon
 
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Default Water heater relief valve -- POW!

buffalobill wrote:
"Temperature/pressure relief valve (T&P)
This valve is designed to prevent a tank from exploding if temperature
or pressure exceeds safe limits, by opening and venting. Unfortunately,
residential valves are somewhat prone to failure. They should be
checked once a year by pulling up on the handle. Water should flow
freely out and stop when you let go of the handle. If it does nothing,
runs or drips, then the valve should be replaced. Banging on the handle
with something hard, like pliers, sometimes will stop drips or even
runs. If not, replace the valve. Hooking up the drain line with a union
or flex connector makes T&P replacement MUCH easier.

People don't like to test their T&Ps. But then, we don't think it's so
much fun to wake up in the hospital, or to patch a big hole in the
roof, either. When water heaters explode, it's catastrophic. People are
injured or die; buildings are severely damaged. Test your T&Ps! And one
more thing: T&P drain lines should go down and out. Never up. If the
valve opens, water will pool there and corrode it shut. Or freeze in
the line in colder climes. We've seen lines plumbed uphill so many
times we've lost count. But there SHOULD be a drain line, usually to
within about six inches of the floor, or plumbed outside. That's code
around here. It's to prevent you from being scalded if the valve should
open while you're standing next to it.

Finally, if water is running out of your T&P line, look for the cause.
It might just be a bad T&P. But it could also signal high-pressure
problems or a dangerously defective control. Don't ignore it!"

this information and more at:

http://www.waterheaterrescue.com/pag...er-safety.html


Got any facts on how many of these explode, how
many people are injured, how many die?

More important, do you have any facts on how many
TP valves just go bad and how many actually
release pressure because of pressure or
temperature build up?

TP valves are a good safety device. Thinking
about them and testing them is a waste of time
that could be better spent paying attention to
your driving, looking both ways before crossing
the street, getting the ladder steady before
climbing, putting the under counter chemicals out
of the kids/grandkids reach, etc. etc.
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