Got a new hot water tank about 6 months ago, put it in and noticed the blow off valve was leaking. Thought maybe it's a bad valve so I put my old one on it and it does the same thing. Got an expansion tank put it in on the cold water side and it solved the problem temporarily but now we are back to it leaking out the blow off valve. Went in the crawl space and turned down the water pressure. No luck then I turned down the temp to 125 still no luck. Any suggestions before my crawl space turns into an indoor pool. Please help

What is water pressure?

Not real sure. I don't have a gauge, but I do know I have the screw on the prv almost turned all the way counter clockwise to the point that it seems as if it is about to fall out.

Quote:

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Not real sure. I don't have a gauge,

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No way to do business.

Pick up pressure gauge so you know what the water pressure is. Cost should be $10-15.

The "blow off valve" is a T&P (temperature and pressure) valve. I could be mistaken but I believe unscrewing increases the pressure.

It is at 30PSI

That is not high enough pressure to cause the valve to open on pressure, so you need to check the temperature, and if it is below the rated value you could need a new valve or you could have scale or dirt on the valve seat casing a leak. That valve should be under warranty, so if the temperature is set below the pop-off value you should call the dealer and get instructions about getting a new valve.

Just check my T&P. It specifies 150 lbs and 210 degrees. You should not be anywhere near that.
I have trouble believing you have two defective T&P valves.
You said you installed an expansion tank.

Must be something else going on.

Do you have a heat check nipple on incoming the cold side piping?

If you have an anti-backflow valve on the incoming side then the expansion from heat would cause it to leak. hkstroud is right-it's very unlikely that two valves are bad.