Water heater pop off valve issue


3 days ago I noticed water leaking out of the pop off valve on my three year old hot water heater. My first thought was bad pop off valve so I replaced it. The problem persisted. Then I thought maybe the thermostat was sticking on and over heating the water so I bought a thermometer and check the water temp at the closest faucet to the tank and the water was 130 deg with the tank set on 125. I then thought I must be having water pressure spikes so I bought a pressure tester and screwed it into the pop off valve outlet and just left the pop off valve open. Initially there was only 75 pounds of pressure. I went back and checked an hour later and the gauge showed the pressure had been as high as 160 pounds. I thought ok my water pressure regulator had bad so I replaced the regulator coming into the house and the pressure was 60 pounds initially. I come back and hour later and the pressure gage had gone up to 200 pounds which tells me if the gauge had not been there the pop off valve would have again let water escape as it is designed to pop at 150 PSI or 210 degrees. The hot water in my house is not scalding hot by a long shot.
Where do I go from here? Why is so much pressure building up in my water heater?
Thanks Joe
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do you have a anti siphon valve at the water line entrance? if so you need a pressure tank.
with no abilty to backflow when your heater heats water it expands and causes the valve to open.
if not you need a pressure regulator valve installed at the entrance
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I have a regulator coming into the house which I replaced today.
Why would I need an expansion tank now when there has not been one for the last 9 years I have owned this house and it has not been a problem up till now? What has changed? Joe

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Joe wrote:

some areas require anti siphon valves or check valves when plumbing is worked on or homes sold.
say you have a garden hose in a swimming pool filling it.
the water goes off, suction will pull water from your pool, it might be yuk dirty and flow to your unsuspecting neighbors.
so a check valve is now required at home sale time.
this makes the plumbing in your home a sealed system. when you hot water tank heats water the pressure increases sometimes dramatically and the valve opens.
a pressure tank absorbs the change in pressure
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Ok I grasp what the pressure tank does and it makes perfect sense. I can see how this would solve my problem. I also understand why codes would have check valves. I do not know if my house has one or not. What I do not understand is why everything has worked just fine for 9 years and now all of the sudden I am going to need an expansion tank. My HWH sits right by the garage entrance to my house and the drain dumps water on my garage floor if it dumps water. I walk right by this every time I come in my house so I would have noticed if this had happened before but it hasn't. So why has thing work just fine up till now without an expansion tank? Joe

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Joe wrote:

Some PRV's have a "bypass" check which will allow a trickle of water to go back to the street *if* street pressure is low enough. But over the years, the bypass port gets clogged and no longer works. Then the pressure skyrockets. This is the reason that Codes require a thermal expansion tank in the presence of a PRV, whether or not it has a bypass.
So, get thee to yon BigBox and buy an expansion tank.
Jim

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Joe wrote:

Mine has been acting up too. Pressure on hot water expansion makes sense. No pressure spikes on my system as I am on a well. All I did was place a small plastic bucket under pressure drain pipe. It's been mostly dry for several months since I first noted and water heater is out of sight in furnace room.
Frank
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I had the same thing happen. Everything worked fine for years until one day water started to leak intermittently from the relief valve. I put on a new relief valve but that didn't stop it. I lowered the house pressure at the regulator; still no change. So, I installed a pressure tank and the problem went away.
I asked myself the same question you're asking. Why, after all these years, did this problem crop up? I could only come up with two possibilities. 1. My pressure regulator had a bypass valve (orifice) that had plugged. 2. The water company had installed a backflow preventor at the meter (or perhaps changed the meter to a type that has a backflow preventor built in).
I didn't pursue the real reason, but I'm betting it was No. 1.
Harry
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A third possibility is that the mains water pressure has been increased to above the valves relief setting. This would prevent the bypass orfice from being effective. If the main is 150PSI and it is regulated down to 60PSI, the bypass will work only when the house pressure goes above 150.
In any case, a working expansion tank will solve the problem. A waterlogged expansion tank is no longer effective and needs to be drained and/or re-pressurized.
Don Young
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You're correct. In my case, I knew the pressure coming to the house wasn't the culprit. My outside hydrants get mains pressure and, while higher than the regulated pressure, it's considerably lower than the pop-off pressure of the relief valve. It's nice for me to have maximum pressure outside, however, I wouldn't want 150 psi on my hoses.
Another thing to consider is that many homes have anti-hammer devices installed throughout the house. These can offer some of the same protection as a pressure tank. However, if they are the type that can waterlog, you can lose their protective effect over time. The best way to check this out is to completely drain down the system, refill, then watch to see what happens to the relief valve.
It's also a good idea to have a pressure gauge installed so that you can actually see what is happening with the water pressure in the home.
Harry
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Since the an expansion tank will solve my problem I am going to get one tomorrow. I am thinking just a small one or two gallon tank should cover it. Would I be correct to install it in the cold water line going into the water heater or does it mater? Joe

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Joe wrote:

Install on the Cold inlet, after the shutoff valve for the heater.

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That will work. Just make sure that there's nothing else (like a check valve..) between the expansion tank and the heater.
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