We bought our home in November of 2008 in Somerset MA. Since then we've done a lot of remodeling.
I had a plumber come in (who has a master license) and plumb the remodeled bathroom and ad some lines for a fridge.... etc.
From day on we had low water pressure in the house. So he suggested that we have the line replaced from the house to the shutoff... so we did, and since we did that the town comes in and replaces the main from the shutoff to the street.
At the same time he had noticed that the pressure relief valve on the water heater was always leaking, so he suggested getting a brand new water heater. Which we did.
He came in and put a brand new water heater in and the pressure relief valve on the brand new water heater started leaking just as the old one did. So he put another brand new pressure relief valve on the brand new water heater and did that 3 times before he figured it has to be something else.
He then went to the water meter and noticed a pressure regulator and said that could be the problem. He took that apart, cleaned it all out and then put it back into place.
As you would guess... the pressure relief valve on the water heater is still leaking.
In his 20 + years of doing plumbing still has no idea what the problem could be. He did all that work in January of 2009 and we've just been putting buckets under that pressure relief valve and emptying it on occasion.
I've called the town to see if they have any idea of what the problem could be and the guy told me that our neighborhood has average 60lbs of water pressure and he has never heard of anything like this before and has no suggestions.