Is it normal for water pressure to rise substantially while the water heater is heating?

I recently had a new gas water heater installed.

My HOA advised owners that they may need to have their pressure reducing valves replaced/repaired. I purchased a pressure gauge and the pressure seemed to be all over the map. Over time, the water flow from the faucets had decreased also. When first turning on a faucet, there would be a slight burst of water which would quickly decrease. In view of this, I decided to repair the PRV. The PRV is a Wilkins 70 and I ordered and installed a repair kit, that included all new interior parts. I then set the pressure at 65psi, as recommended by my HOA. This seems to have corrected the water flow from the faucets, which is now back to normal.

Now, when the water heater is heating, the pressure rises to about 100psi. If I turn on a faucet in the house, the water pressure lowers almost to normal. Otherwise, it slowly returns to normal. The WH has a T&P valve and I have not noticed any water leaking.

Is it normal for water pressure to rise substantially while the water heater is heating?

I recently had a new gas water heater installed.

My HOA advised owners that they may need to have their pressure reducing valves replaced/repaired. I purchased a pressure gauge and the pressure seemed to be all over the map. Over time, the water flow from the faucets had decreased also. When first turning on a faucet, there would be a slight burst of water which would quickly decrease. In view of this, I decided to repair the PRV. The PRV is a Wilkins 70 and I ordered and installed a repair kit, that included all new interior parts. I then set the pressure at 65psi, as recommended by my HOA. This seems to have corrected the water flow from the faucets, which is now back to normal.

Now, when the water heater is heating, the pressure rises to about 100psi. If I turn on a faucet in the house, the water pressure lowers almost to normal. Otherwise, it slowly returns to normal. The WH has a T&P valve and I have not noticed any water leaking.

Water and other liquids always expand when heated. Do you have an expansion tank on the cold side? If there is a check valve in the city piping, without an expansion tank you will always increase pressure when the water heats.

No, I do not have an expansion tank and did not have one with the previous two water heaters. In fact, I had never heard of an expansion tank until recently.

No, I do not have an expansion tank and did not have one with the previous two water heaters. In fact, I had never heard of an expansion tank until recently.

You only really need one if the water system has installed a backflow valve at the meter.