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Old 09-21-2015, 01:26 PM  
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Default Mystery water heater problem

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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Old 09-21-2015, 04:22 PM  
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Temp, pressure or defect...pick one ;-)
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Old 09-21-2015, 04:48 PM  
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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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Old 09-21-2015, 05:22 PM  
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check valve on the cold side .set the expansion tank lower than the pressure coming in to the house
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Old 09-21-2015, 06:23 PM  
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Quote:
Originally Posted by justme View Post
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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Old 09-21-2015, 06:28 PM  
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Quote:
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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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Old 09-21-2015, 07:11 PM  
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Would one or more water hammer arresters do the trick?
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Old 09-21-2015, 07:22 PM  
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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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Old 09-21-2015, 08:24 PM  
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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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Old 09-21-2015, 08:50 PM  
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Quote:
Originally Posted by beanburner
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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