Water heater Woes
If you have a thermometer that goes that high you can measure the hot water temperature directly after letting the water run awhile. Never run a glass thermometer all the way to the top or let it rise fast otherwise it could explode and send mercury or staining fluid all over the place.
Are the spikes to 140 PSI very short and only when someone turns the water off after using? Could be just the effects of water hammer but could still make a relief valve open momentarily. Somehow a standing (or ambient) 60 to 80 psi in your water system looks high to me and a pressure reducer unit on the cold water line just inside the house (before the meter if that is also inside) would be appropriate.
Sometimes the main shutoff is outside and perhaps buried in your lawn although it should have a control rod you can see. If that is the only shutoff, have another shutoff installed inside. A water heater should have shutoffs on both inlet and outlet.
Last edited by AllanJ; 12-07-2008 at 10:41 AM.