water pressure

I installed a new 50 gallon gas water heater and the water pressure seems to be too high and the releif valve keeps letting out water. I had a plumber come by and tell me the water presure was too high. I have lived here for two years and now the water pressure is too high? Where can I buy a regulator or should I go with an exspansion tank? Where should the regulator be installed? The tank? Where can I buy a regulator?
My house was built in 1997.
Thanks
Ron

The first thing you should buy is a pressure gauge. What is "too high"? That means nothing until you put a psi with it.

Relief valves on water heaters are usually set at 150 psi. It is hard to imagine a municipal supply pressure that high. Maybe your plumber doesn't want to replace a defective valve. You shouldn't have a problem up to at least 90 psi.

From what I have seen here, the biggest complaint about regulators (Pressure reducing valves, PRVs) is that they have to much pressure drop at high flows. The Conbraco Model 36 H (About $130 at Grainger in the 1" size) is the highest flow rated model that I have seen in that size.

With a regulator, you will need an expansion tank because expanding water when the water heater heats cold water can't escape back to the water source.

Plan on about $200 for the regulator and expansion tank if you do it yourself, or $400 or more if your plumber does it. There are cheaper valves that will also work and you will doubtless get suggestions here.

When water heats it expands. Unless you have a backflow preventer in the supply line, the expanded water just is absorbed by the the water main and causes no problem. I understand some localities are installing meters that have a backflow preventer built into them and if you install a PRV, this is also a backflow preventer. In either of those cases, you need to install an expansion tank in the supply line before the line reaches the heater. This is called a closed system. It's just like the system in newer cars that have that plastic bottle to catch the water that expands when it is hot. If you have a closed system in your home, but do not have an expansion tank, the water pressure will quickly exceed 150 psi when the heater kick in. This will cause the TP valve to trip to relieve this excess pressure. I don't know why this is just now occuring unless the old TP was not working and didn't relieve the excess pressure. Just installing the new tank would not create the problem. I will disagree with the cost of a PRV and expansion tank. You can get a PRV and an expansion tank for about $50 each. Installation is quite simple, and if you can sweat a joint, you can do this. I would go ahead an install the pressure gauge next to the PRV so you can set and monitor the pressure. The gauge will cost about $10 and with necessary fittings to reduce the gauge size to copper and a few ordinary copper fittings costing perhaps another $5, you'd have no more than $120 invested. I'd set the PRV to about 60 pounds. The expansion tank has to be filled with air to the same pressure as the PRV is set to, and this is done with a regular air pump. To do this, Watts recommends a hand pump, but I used my air compressor, an air gauge, and was careful not to put too much air in the tank. These supplies are readily availble at the Big Box Stores or plumbing supply houses.