High water pressure!

I am getting very high pressure readings in my house at present. The pressure is approx 120 lbs with nothing running in the house. When the hot water tank turns on the water pressure is getting to 140 lbs and higher.
The problem was found because the hot water tank is discharging through the pressure relief valve.
There is a pressure regulator installed right as the service enters the house but it does not seem to be working. It has an adjuster on the top but I don't know which way to go with it. From the only view I have (its behind drywall) it does not have any markings or instructions.
Can anyone advise? Do I turn the screw into the regulator or away from it? It has a bell shaped brass housing that sits above the water supply line. The adjusting screw is on top. Does it need to be replaced?
Thanks - Tom
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On 10/04/04 "Me" snipped-for-privacy@Chongo.net asks in part:

Classic example of Thermal Expansion. Install an expansion tank on the cold water piping close to the water heater. Check them out here: <http://www.wattsreg.com/scripts/baserun2/baserun.exe?_cfg=./db/wattsreg-p roducts.cfg&_sn=wattsreg-products&_fil=alltrim(cat)%3d'Expansion_Tanks'.an d.alltrim(family)%3d'Water_Heater_Installation_Products'&_tar=_view3>
Doug
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New pressure valve fixed the problem.
asks in part:

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did it????
you could need backflow and expansion tank still.

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