Water Heater Relief Valve firing intermittently

Hello,
I recently discovered water pooling on the floor below the relief valve on the water heater. It appeared to have a slow drip at the time, so I had a plumber out who replaced the valve with a brand new one. To watch for any further problems, I put a bucket under the discharge pipe for the relief valve.
Intermittently, I'm finding somewhere about 1-2 cups of water in the bucket. I empty it and put it back and hours later I find another few cups. The valve is NOT leaking constantly, it appears to be firing occasionally apparently.
The water heater is 5 years old. The plumber checked the pressure at my water meter and at that time it was 80 PSI. I think I must have a backflow preventer, although I don't see it (but then again I'm not 100% sure what it should look like) because I'm quite certain the city code requires it. The code says:
"The City of Sioux Falls potable water system shall be protected from all
cross connections by a backflow prevention assembly in accordance with the City of Sioux Falls Plumbing Code and approved by the City of Sioux Falls Engineering Division."
From my understanding a "cross connection" would be my house and their city water at the water meter I guess.
By the way, turning down the temperature setting on the water heater appears to make no difference.
What is the most logical cause? Could it be that there is a spike in pressure from the city occasionally? Would a expansion tank on the cold water line going into the water heater be a good idea? Is 80 PSI an acceptable value?
I can catch the water in the bucket, as long as the volume doesn't increase or frequency doesn't increase, but that doesn't address the root cause.
Ideas?
Thanks,
Greg

I think the problem is the TP has begun to fail. Get a new one and replace it. A crossconnection is when you tee off of your supply line for a sprinkler system and prevents contaminated water from the sprinkler line from getting into your household supply. You might consider a pressure regulator valve because 80 psi is too high. It should run 40 to 60 psi. I don't know if that is related to you TP valve failure or not. A pressure regulator is usually placed in the supply line before where it enters the house and before any fixture.

relief valve

Also when the clothes washer cycles, the on and off when the water shuts off abruptly, it jolts the spring on the relief valve and weakens it....

Do you have an expansion tank in your system? Assuming that you have a check valve, it is required for proper operation of the system. Reason is, you empty some hot water from the heater, replacing it with cold. Turn off the faucet. The water heats up, expands and has nowhere to go except build up pressure and pop the relief valve. Do this often enough, and you wear out the relief valve along with those spurts of water...

If you have a tank, make sure it is not waterlogged (it should sound hollow). If it does sound like it is full, remove the air valve cap - see if water comes out. If it does, the tank is shot. If it doesn't, then use a tire pressure gauge and check the pressure. If it is above zero, then shut off the water to the house, open a valve until the water stops running, then check the pressure again. Fill to around the normal water pressure with a pump. Check to see if it holds for awhile. If it does, close the faucet, open the main shutoff and see if it cured it. You probably need a new expansion tank, or if none is there, install one. My unprofessional opinion.

Thanks

No, I don't have an expansion tank.
Today while I was reading your replies, I called the city to talk to them.
The pressure coming into the house is 80 PSI which is pretty high. On our side of town they've expanded so fast that the pressure is pretty high right now on some of our houses because some of the other newer homes had low pressure, so they did things to increase pressure, inadvertantly increasing it too high for some of us who had adequate pressure already.
Our house was built in 1999 and has a backflow prevention device, as required by code. However, we do NOT have a expansion tank/bladder device before the water heater. This seems to be causing the problem. The rep from the city said a lot of people have been adding them recently and they are being added to new construction since the problem is so common.
So, I guess I'll have the plumber add one of those.
The only other thing I might discuss with them is maybe a pressure regulator right at the water meter to protect the whole house fixtures from the high pressure, unless this bladder will do anything for the rest of the house.
Thanks for the help.
Greg

In this application, the bladder tank does not need to normally hold any water at all - it is used to give the expanding water held in the system a place to go without stressing the fixtures and relief valve. In a well system, a bladder tank is what holds that stored water under pressure in between pump cycles. The small bladder tanks used for expansion problems often come charged for heating systems which is usually around 15 pounds. With 80 pounds, you would stress that bladder and mostly fill the tank with water, leaving little room for it to expand and hold some from the water heater causing the expansion, so, make sure you increase that pressure to around the system pressure. Then, you will not over extend it, and there will be room for that water to go.

Jim Nailed It

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