its at the top of the pressure vessel, so you will probably have to stand on a chair to see it, if you depress the pin and it hisses you probably dont need to pump it up, a can of worms could be opened here because to pump up the vessel you need to open the pressure relief valve and leave it open to pump water out of the expansion vessel, but the relief valves very often drip or totally let by once they have been opened forewarned and all that
john
March 2010