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What you're describing is the result of your recent work. The water in the water heater expands as it heats up. Before it would expand back into the water main. Can't do that now with a check valve and your starting (tank full of cold water) pressure is higher now too because of the booster pump. The fix is to install a thermal expansion tank (see attached pic) on the cold water line near the heater. It must be rated for a water heater not a hot water heating system.