# Mystery water heater problem



## Johnny Canuck (Feb 24, 2015)

I've got a friend with 2 water heaters, side by side but not connected. Ones for the upstairs apartment, one for the downstairs apartment.
A couple of weeks ago his downstairs water heater started blowing off at the T&P so he had a guy in to replace the water heater and add an expansion tank. New tank, same problem so he replaced the T&P twice, same problem. Called GSW they said change the thermostats. He called me to do that. Same problem. Got GSW to agree to a new tank. I installed it, put the expansion tank on the cold supply instead of the hot that the other guy put it on. Just got called and it's still repeatedly blowing off.
My first thought was PRV but the house is at a constant 60 psi and the other water heater is fine. 
Am I missing something?


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## 760GWS (Mar 16, 2015)

Temp, pressure or defect...pick one ;-)


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## justme (Jul 4, 2012)

Well if it's doing the same thing with the new heater that it was with the old heater then you have another issue and more than likely you're getting a pressure spike . I would get a tattle tell gauge to put on a hosebib near by and see what it spikes at. I call them a tattle tell gauge because they have a red needle that will show what the highest pressure the line has been exposed to while you're not looking , the red needle will stay at the highest pressure achieved even after the spike corrects itself. Good luck.


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## beanburner (Apr 30, 2012)

check valve on the cold side .set the expansion tank lower than the pressure coming in to the house


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## Johnny Canuck (Feb 24, 2015)

justme said:


> Well if it's doing the same thing with the new heater that it was with the old heater then you have another issue and more than likely you're getting a pressure spike . I would get a tattle tell gauge to put on a hosebib near by and see what it spikes at. I call them a tattle tell gauge because they have a red needle that will show what the highest pressure the line has been exposed to while you're not looking , the red needle will stay at the highest pressure achieved even after the spike corrects itself. Good luck.


I checked again and it was up to 80 then down to 70 a few minutes later.


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## Johnny Canuck (Feb 24, 2015)

beanburner said:


> check valve on the cold side .set the expansion tank lower than the pressure coming in to the house


Never seen anyone around here use a check valve.


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## Cajunhiker (Dec 14, 2009)

Would one or more water hammer arresters do the trick?


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## bct p&h (Jan 19, 2013)

Johns_TPS said:


> I checked again and it was up to 80 then down to 70 a few minutes later.


Is there already a PRV? Either way, looks like you're buying one. When you do put it in, don't be cheap, install a gauge after it.


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## 760GWS (Mar 16, 2015)

WH ea for US & DS apts, but common cold supply? If so, I'm thinking need the large exp tank, assuming 30+gal WHs.

Is that other TNP valve old and stuck closed? Might need to put a gauge on ea WH to compare.


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## plumberkc (Jun 23, 2011)

beanburner said:


> check valve on the cold side .set the expansion tank lower than the pressure coming in to the house


 That's a sure fire way to have your expansion tank fail in under 3 years.


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## plumberkc (Jun 23, 2011)

I'm guessing it's a bad PRV but without more information it's really just a guess.


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## Johnny Canuck (Feb 24, 2015)

plumberkc said:


> I'm guessing it's a bad PRV but without more information it's really just a guess.


I changed the PRV. Time will tell. I'm assuming that both tanks share a common cold supply but in a round about way. The plumbing was not done by a plumber originally so the cold water comes from the PRV around to the water heater. Its tee'd and supplies the washing machine, then tee'd again, one branch going to the problem water heater and the other going through the wall. About 5' further down the wall it re-enters and supplies the up stairs water heater. 
I was wondering if the PRV was wore out if it might be pressurizing the 1st tank supplied which would blow off before the 2nd one could build up. Should find out tm.


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## Debo22 (Feb 15, 2015)

If you are getting various pressure your prv is a goner


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## Johnny Canuck (Feb 24, 2015)

Debo22 said:


> If you are getting various pressure your prv is a goner


That's what I figured but thought both T&P would be blowing off


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## CTs2p2 (Dec 6, 2011)

Maybe the relief is seized on the one that isn't blowing

If that's not the case is be looking at quick close solenoid valves on the plumbing side of the house with the relief issues.. Dishwasher/ laundry slamming the hot water side closed..

If it were my customer I would change the relief on the tank not blowing and size an xtank for both heaters (installed on the cold main right after prv..)


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## CTs2p2 (Dec 6, 2011)

CTs2p2 said:


> Maybe the relief is seized on the one that isn't blowing If that's not the case i'd be looking at quick close solenoid valves on the plumbing side of the house with the relief issues.. Dishwasher/ laundry slamming the hot water side closed.. If it were my customer I would change the relief on the tank not blowing and size an xtank for both heaters (installed on the cold main right after prv..)


Typo and I can't edit my posts anymore so I'll just do this haha


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## Master Mark (Aug 14, 2009)

you said that have already changed out the PRV... 
and you did not get shocked or killed .....thats good..
so its not a crossed ground or an electrical problem
that could be heating up and expanding the water in the plumbing the system

Install the larger thermal tanks on both water heaters...


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## Johnny Canuck (Feb 24, 2015)

Master Mark said:


> you said that have already changed out the PRV...
> and you did not get shocked or killed .....thats good..
> so its not a crossed ground or an electrical problem
> that could be heating up and expanding the water in the plumbing the system
> ...


I never thought of electrical. I'll find out today if the PRV did the trick. If not I'll get a sparky friend to check the electrical


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## Master Mark (Aug 14, 2009)

Johns_TPS said:


> I never thought of electrical. I'll find out today if the PRV did the trick. If not I'll get a sparky friend to check the electrical



I about got myself kilt a long time ago when I tried to change out a prv in a basement and when I took the union apart on the prv all the lights in the home flickered and some pretty sparks jumped across the union.... 

No ground in the home or a reversed neutral....so the galvanized pipes were somehow grounding and expanding the water in the system ??:blink: 

It was about the same kind of mystery thing you are presently going through with the t+p valves popping off for no reason....

I was wet and kneeling in water when I did this and I think the only thing that kept me alive was the insulated well pump pliers I had in my hand....

pretty sparks in the dark flashing off right in my face...:blink:.
a very memorable experience....:yes:.


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## plumberkc (Jun 23, 2011)

Master Mark said:


> I about got myself kilt a long time ago when I tried to change out a prv in a basement and when I took the union apart on the prv all the lights in the home flickered and some pretty sparks jumped across the union.... No ground in the home or a reversed neutral....so the galvanized pipes were somehow grounding and expanding the water in the system ??:blink: It was about the same kind of mystery thing you are presently going through with the t+p valves popping off for no reason.... I was wet and kneeling in water when I did this and I think the only thing that kept me alive was the insulated well pump pliers I had in my hand.... pretty sparks in the dark flashing off right in my face...:blink:. a very memorable experience....:yes:.


Did you find out what idiot was responsible for the electrical?


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## MACPLUMB777 (Jun 18, 2008)

Master Mark said:


> I about got myself kilt a long time ago when I tried to change out a prv in a basement and when I took the union apart on the prv all the lights in the home flickered and some pretty sparks jumped across the union....
> 
> No ground in the home or a reversed neutral....so the galvanized pipes were somehow grounding and expanding the water in the system ??:blink:
> 
> ...



I had the same sort of thing happen when I started a repipe as started cutting old galv, out got sparks when pipe was cut it drop almost all lights and power in the house, :furious:

of course the HO wanted to blame me for the problem,


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## plumbdrum (Nov 30, 2013)

Master Mark said:


> I about got myself kilt a long time ago when I tried to change out a prv in a basement and when I took the union apart on the prv all the lights in the home flickered and some pretty sparks jumped across the union....
> 
> No ground in the home or a reversed neutral....so the galvanized pipes were somehow grounding and expanding the water in the system ??:blink:
> 
> ...



Had that same problem years ago. When I broke the meter connection I was getting a tingle and arcing was jumping across the meter. I blew out a few things in the house and lights were flickering. The neutral was lost in the panel. Scary!!!!


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## Johnny Canuck (Feb 24, 2015)

Talked to the HO today and the problem seems fixed. I mentioned a couple other things for him to watch out for that I noticed that I'd like to fix later on .


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## Master Mark (Aug 14, 2009)

plumberkc said:


> Did you find out what idiot was responsible for the electrical?



I am pretty sure it was a do it your selfer that tangled with knob and tube wireing and somehow tried to update the system and wired something in the new box backwards..... 

after this mis-hap happenned to me, the lady claimed that she noticed when she put her hand on the stainless steel sink and turned on the disposal she got a small tingle shock from it....

they had someone come in and make it right .


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## Flyout95 (Apr 13, 2012)

Well, I'll never cut into galvanized again.


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## bct p&h (Jan 19, 2013)

Flyout95 said:


> Well, I'll never cut into galvanized again.


I've had it happen on copper when I was changing out a broken gate valve to a ball valve at the meter once. Not quite as bad as others have mentioned, but still saw the arch when I cut the pipe.


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## Flyout95 (Apr 13, 2012)

*retires*


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## Redwood (Sep 8, 2008)

I wrote this article on my site about open neutrals some time ago...

It's worth repeating the link for you guys to read...


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## justme (Jul 4, 2012)

I cut a copper freon line a few years back to install a new system in my own house and found out the hard way that the neutral coming in from the power company at the mast was very very loose. Needless to say I had all the wiring checked out by a licensed electrician friend of mine and we traced it down to the overhead line coming to the house , both hots were tight as can be but the neutral was barely making contact, so since the neutral and ground are bonded in the panel that means everything was back feeding into the ground and anything else that was grounded. From this point on I shut down all electrical before I work on anything , pretty pale blue sparks lol . But there has been some very good advice on PZ about using jumper cables to put a bypass around the area of pipe that you're cutting .


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## MACPLUMB777 (Jun 18, 2008)

760GWS said:


> WH ea for US & DS apts, but common cold supply? If so, I'm thinking need the large exp tank, assuming 30+gal WHs.
> 
> Is that other TNP valve old and stuck closed? Might need to put a gauge on ea WH to compare.


The lower water heater is going to have slightly higher pressure just because
of elevation, therefore the t&p will open first relieving excess pressure
but before the upper ever gets high enough to open :whistling2:


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## sparky (Jan 8, 2014)

plumberkc said:


> That's a sure fire way to have your expansion tank fail in under 3 years.


Exactly


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