New Pressure Tank in Hydronic System Issue

[frank1492]

I just installed a new pressure tank in my hydronic system. It said it was pre-charged to 12 psi. When refilling the system I think I did a good job of eliminating the air as there is little noise when the circulator is running, plus there is a Spirovent installed. I like to keep the system pressure at between 15 and 20 lbs. but I noticed the pressure seems to drop back to 0 quite often. Then when I add water, the pressure seems to rise very quickly. The only thing I can think of is that I have no air cushion. I did not check the tank pressure before installing. What is wrong and what should I do? I'd like not to have to drain the system again. Thanks in advance. Frank

[frank1492]

Just heard a loud "whoosh" and the pressure has gone to zero again. Nothing is leaking. Add that to the clues.

[ransley]

Do you mean the pressure gauge on the boiler, how much does pressure change from high to low, is your house 1 or 3 story, with radiators I can not go to zero unless my system is empty, to keep my 3rd floor radiator full of water I need near 12-15lb and only increase a few pounds as water heats. Maybe a bad gauge, what was wrong with old tank, to small a tank and pressure can jump when heated and be erratic, when our boiler was changed the attic expansion tank was eliminated and a basement tank installed, but we eventualy needed two tanks as one was to small and pressure jumped 15-20lb with every heating cycle.

"the wall" is where boiler pros are.

[frank1492]

Sorry I wasn't clear. This is a *closed leg* with a circulator, pressure tank and gauge. (Runs through a heat exhanger or tankless heater, heat supplied by circulating steam boiler water- old boiler.) Has always worked perfectly with identical components until the old tank sprung a leak. I realize the ideal situation would be to have a pressure reducing valve and backflow preventer permanently attached but letting in the water manually on rare occasions has always worked fine. So the only thing that's new is the new pressure tank, same capacity, style as before. As I say, when you let water in now, the pressure rises very quickly as if there was no air cushion.

[Doug Miller]

That suggests strongly that there is not in fact an air cushion. By any chance is there a valve between the gauge and the air tank? And is that valve open?

[frank1492]

The tank is on a tee in the loop and the gauge is on a separate tee. There is no valve between gauge and air tank. I know, it's puzzling. I really thought someone would have a quick answer. Of course I can always disassemble everything and start over, but first I guess I should ascertain if there is air in the tank at all. It seems I should mention something: When filling the system, I accidentally let the pressure get to about 80 lbs, but *only* momentarily. The max tank pressure is supposed to be 75 lbs. I know it's a stretch but any chance the bladder was damaged?

[Joe]

[Grumpy]

is these system steam or water

[Ed Pawlowski]

It would not be steam in a residence with that pressure. Now would steam have an expansion tank anyway.

[Grumpy]

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[Ed Pawlowski]

Only way would be for a defective fill/pressure regulator valve allowing full incoming pressure. Or, he is making steam in that water boiler because it is not circulating and shutting down the burner.

[Grumpy]