Water heater pressure - drip

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ErikU

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I installed a new 50 gal water heater in my house about 2 years ago. A couple months ago I noticed that the pressure relief tube was dripping about a cup of water a day. I replaced the relief valve and still have the same drip. The temp is measured at 120 degrees. I purchased a pressure gauge today and read 65psi for the house. At the bottom of the hot water tank it goes off the scale at over 100 PSI. So I assume I have a pressure problem.

What I find strange is that I do not have a check valve or regulator on the incoming line, so I don't really understand why this would have changed a couple months ago.

I guess the solution is to install an expansion tank at the cold water line. Does 100 PSI on the tank sound out of line? Thoughts?

Thanks,

Erik
 

Cal

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Have been having the same situation for many of the customers.It was explained to several of us plumbers as follows," The newer water meters are not allowing back-pressure.Due to many quick-close valves in the newer houses,this causes a "pressure bump". The only place to release is the p&t valve on the heater." Have used several expansion tanks and solved the problem. The tank calls for the pressure to match the incoming water pressure. Good Luck !
 

hj

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heater

Your new heater probably has "heat trap" devices in the inlet and outlet ports of the heater. They are "check valves" so can cause thermal expansion. But if that is your problem, an expansion tank on the inlet to the heater will not help it, unless you remove the heat trap from the inlet side, and if you do that you do not need the expansion tank, as long as you do not have a PRV or check valve to trap the pressure in some other way.
 

Kevin @ ProSpex

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Dripping T/P valve

To reduce the potential for cross-connection contamination of public water supplies by end users, more and more building departments and municipal water service providers are requiring the installation of backflow prevention check valves on both residential and commercial water supply lines to create "closed" potable water systems. Water in the supply and distribution piping downstream of these check valves cannot move back toward and mix with the public water supply.

Water expands as much as three to four percent in volume when it is heated depending on the initial and final temperature. If there is no demand for hot water, the expanded volume of water has nowhere to go and, since liquids cannot be compressed, additional pressure in the potable water system increases. In an older "open" system without a check valve on the main water supply line, this expansion was taken up by "pushing" the water in the supply and distribution piping back into the municipal water system.

This additional pressure resulting from heating water can cause temperature/pressure relief valves on water heaters to open to relieve the pressure. This can be more than simply a nuisance, it can damage water heater components and create potentially dangerous conditions. Although rare, there have been instances where the internal flues in gas or oil-fired water heaters have collapsed due to the unrelieved crushing pressure in closed systems.

The solution to the problem of overpressure from thermal expansion in closed systems is the installation of an expansion tank on the water heater cold water feed line between the water heater and the feed line isolation valve. A properly sized and properly installed expansion tank will accommodate the increased pressure in the system even if there are "heat traps" designed into the piping system.
 

ErikU

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It sounds like the expansion tank is the way to go, but I am a little confused that all of this changed suddenly a couple months ago. My house was built in 1965, and there has been no recent plumbing work and nothing going on out in the street. Is it possible that the heat trap on the water hear has failed? I guess I will just have to try the expansion tank and see what happens.
 

Kevin @ ProSpex

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T/P valve

It's possible that your water utility repalced your meter with one which incorporates a check valve. However, if they did, I'd think that they would have let you know. You might want to contact them and ask.
 

ErikU

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If they did, wouldn't I see that same 100PSI+ pressure in the entire line in my house? I only see it at the water heater outlet. The cold water line measured elsewhere was at 65 PSI.
 
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