Pressure Valve Leaking

I have a hot water boiler pressure valve (30 PSI)which is leaking. I have replaced it twice. I have tried turning off the water incoming source and the out water domestic hotwater (not the heating zones), and still leaking. I checked the pressure tank and it was at 18 PSI, I released some of the pressure down to 12 it lessened pressure off the system and the leaking stopped. The pressure tank again went up to 18 and again I put it down to 12 to stop leaking. Now I get no reading from the pressure tank (hope I did not mess it up), but there is pressure in it. The pressure tank is about a year old and sounds OK when I knock on it, hollow on top, full on bottom. When the circulator is on the pressure seems to come down to somewhere between 20 and 25 when the circulator stops the pressure seems to rise and pressure release valve leaks. Any suggestions? Thanks in advance.
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Seriously, you need to stop messing with it before you make a minor repair turn into a very expensive repair. Call in someone that knows about hot water systems. Bubba
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Is the water feed off, you jump from 12 cold to 25 hot. I had a new boiler and expansion tank a few years ago and went from 12 cold to 35 or so hot, and was leaking the relief also, the installer put in an expansion tank that was to small, solution was he added a second tank, now its fine. But I dont know if this could apply to you as I had a much greater jump in pressure. You only need enough pressure or altitude to get water to the highest radiators, try lowering it till it is sorted out, could your gauge be bad reading low
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how about MAYBE: you have a bad pressure gauge misleading you? or MAYBE rust or dirt is bothering your pressure relief valve, with insulated gloves open it up and flush it out its scalding water and debris. hunt down your nearest old time experienced plumber in your neighborhood to call on. your required pressure when hot to get to how many feet to the top radiator needs to be marked with a permanent marker near your gauge by you for your system. i need 25 pounds when running and heating to get to the top of my third floor radiators from the basement boiler IN MY SYSTEM for example. you need to search google for the manual pdf for your boiler, read about your system, discuss the repair and seasonal maintenance of your particular accessories and how they interconnect with your friendly local expert, and keep the manuals for the various devices dry in a big 2-1/2 gallon ziplock bag convenient to the devices. you have an interesting system which makes heat and hot drinking water.
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Try changing it to a cold water boiler system and see if that lowers the pressure.
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