This is a classic symptom of a pressure regulator valve with a pin hole leak in the valve diaphragm. Call a plumber before a pipe lets go and floods the home.
STOP
I think you are all wrong - Don’t spend $$ on a new regulator yet
More testing is in order
If you have a regulator you better have a small expansion tank - about the size of a 3 gal. round container. It should be near the regulator but not requried to be so. In short it could be any where
First kill the power to the water tank completely electric or gas. Then run the hot water until it is cold. Check the pressue in the expansion tank and make sure it is as per mfg…
Now check to see if the pressure goes up. If it does it is a bad regulator
The reason for the above - the water pressure in the home with just one degree of temp change can go very high if the system is a solid. The regulator keeps it from going back to the street and with no leaks up goes the pressure large and fast
If it were a gas one degree is equal to one pound but this is a solid and a gas so with a bad or no expansion tank who knows but much larger
Remember you do not have to use hot water to have the tank turn on
This is another reason for HI to know basic plumbing and to monitor water pressure
Now as an additional check in case both the regulator and the expansion tank are bad turn on the hot water tank and see if the pressure goes up
The purpose of the expansion tank is to take care of the expansion from the hot water tank temp changes
Hope you have not spent $$ in the wrong spot yet
Good luck
rlb
I just want to give you update.
As we diagnosed and with the help from this forum, the water pressure regulator failed. We shut the main valve off just want to make sure the pressure is from street. (that was the bad move) But that valve wouldn’t be turned back on. We called the plumber, he told us that happens a lot to those gate valve. Then he put the bill in front of us. That is total $1000+. We were shocked. But we had no choice since we couldn’t live without water. That was last Saturday night, even we called another plumber, it would came up similar amount. we knew that was the good time to be ripped off. He also proposed to replace the water heater which was leaking from the top. (I don’t know why it would leak from the top) We wanted to replace that water heater anyway, so we agreed. It came up another $1000. After some bargain, he agreed to give us $200 discount.
We scheduled for Tuesday. I took the day off. They didn’t show. When I called, they said it was for Wednesday. We rescheduled for Saturday. Today, they showed up on time. After 3 hours, works was done. Before they left, we noticed the main valve was leaking. They agreed to replace it next week. (since they don’t have extra valve on truck?)
After they left, we found out they replaced my 50 gal with 40 gallon with only 6 year warranty on the tank. We called them, they agreed to fix it next week.
Now you know why we don’t like plumber(Plus we had another bad experience with plumber before.)