Here in the northeastern US, I performed some routine annual maintainance on my domestic natural gas furnace/boiler by removing and cleaning out the burners and testing the pressure release valve. Water came out of the valve -- so far, so good.  But then it wouldn't STOP coming out because crud had accreted to the valve gasket so that once opened, it no longer formed a tight seal when shut.  So I replaced the entire pressure release valve.  Prior to replacing it (back when it still formed a tight seal and didn't leak) I never had problem with water leaking out this valve, presumably because boiler pressure never built up enough to exceed the release valve's psi rating (30 psi).  (Either that, or I did have problem that I didn't know about because the release valve was, unbeknownst to me, not functioning and just remaining shut tight regardless of the boiler pressure.  I'd rather not think about that.)  But now, when I run the boiler, pressure builds to 30 psi without fail, causing my new release valve to operate and begin releasing water.  So, my question is why is the boiler doing this now?  The only difference between what I did this year and in past years is that I tested and replaced the release valve.  Cleaning the burners can't have caused this problem.  Or is this pressure situation likely to be unrelated to anything I've done?  I lack the expertise needed to diagnose the reason for this malfunction, and I hope one of you knows the answer.
Other potentially relevant info:  this bioler also has a diaphragm-type expansion tank, and between the tank and the boiler is float-type air valve (45 psi), which has been emitting a very small amount of water, kind an almost impercetible seep. Honestly, I can't really tell you whether the behavior of the air valve is new or not, but I suspect it's not new, given the green/aquamarine staining on it's copper exterior, which suggests that's been going for a while.  The regulator on the cold water intake is of the 12 psi variety.

We're enjoying mild November weather at the moment, so I have the entire system shut off.  If for some reason you conclude that I ought not to turn it back on under the present circumstances, that I'm sitting on a powder keg that's ready to pop, that the situation is dire, and that, in that light what I'm doing now could be called "fiddling while Rome burns," to an extent that makes you want to scream, "Call a heating professional to your house ASAP to avert disaster,"  then that info would be very welcome.

The biggest mistakes I see with situations like yours, is many people calmly screw a plug into the relief valve outlet. I've even seen pictures of a second relief screwed into the outlet of the first. There's the less common practice of installating a relief with a much higher setting, or simply removing the relief altogether. "These stupid things always leak..."

Check the expansion tank - the air pressure should be checked with the tank valved out of the system. The pressure should be maybe 5 PSI higher than the fill pressure of the system. If you depress the little air valve with a screwdriver, and you get water & air, or just water coming out, then the diaphragm is shot. Another problem is the make-up water PRV is passing or set too high. Does this boiler have a domestic hot water coil in it? A leak in this coil will let the higher pressure domestic water leak into the boiler side.

The air separator, like the relief valve, is just doing it's job. Every time the relief valve burps out some water when the system heats up, the little make-up valve feeds water in, when the system cools down. The dissolved air in this cold make-up water is what's being discharged by the air vent.

MORE NEWS