Boiler Overpressure

Toneloc

I have one that has me stumped. A few weeks ago I noticed my when my boiler was running for my indirect tank, I was seeing an increase in pressure. I suspected my expansion tank, but it was one of those Amtrols with the color change cap and it looked white, so I ruled that out. Then I considered maybe a small leak in the heat exchanger in my indirect that was allowing domestic water to leak back. Fast forward to heating season starting and found when my baseboards were calling for heat, was seeing the same rise in pressure. To double check this, I isolated the indirect….and was seeing same rise. Up to 30 or 40+ psig! Not sure how the relief valve wasn't cracking.

I had one of those Amtrol Filltrol brass pressure regulators with smallish 2 gallon expansion tank, so decided to replace this with a traditional watts pressure regulator and new Amtrol no 30 tank with nearly double the capacity of the original. (pressure checked this before install and it had 13.8 psig so I reduced to 12 psig…..also tried adding a few lbs back with no change). Those white caps lie, cause the tank was totally water logged with zero pressure. I emptied it and refilled it with air and could hear the slow leak. I thought I had my smoking gun.

Started back up yesterday and still seeing high pressure after a several minutes of operation. Seems like it's circulating hot water fine. Hotter water on the supply and slightly lower on the return as expected. Even though I'm seeing pressure as high as over 40 psig, it's not tripping the relief valve.

I had a brass hose drain cap lying around and old pressure gauge, so I drilled and tapped this for 1/4" NPT and put this over the drain and opened it when had over 40 psig. It read 25 psig. The gauge old and maybe not totally trustworthy, but another data point.

I also reduced my aquastat from 190F to 180F with no improvement in overpressure readings on the tridicator gauge.

I don't quite understand how all the internal passages in the boiler work, but I can't understand how this can be possible. Tapping on the expansion new tank can hear there is empty air space at the bottom.

So my next step is to try replacing the tridicator gauge….but not holding my breath.

Is there some possibility that there is internal blockages in the boiler that are making higher pressure in some sections but still letting water pass around in others?

Thanks head for any help/suggestions.

Tony

Grallert

Hard to be certain but if your relief valve is good, again hard to know not being there. But if its good and your expansion tank is good I think you're on the right track replacing the gauge. I'm more apt to believe the relief valve and the pressure regulating device than I am to believe the often cheepo gauges often supplied with the boilers these days.

Toneloc

https://forum.heatinghelp.com/discussion/comment/1907292#Comment_1907292

Thanks for the quick reply. I probably should have mentioned that this boiler is likely 30 years old. Slantfin 90,000 btu. So that gauge and relief valve likely original too.

Grallert

The three components I found that would fail and give no real evidence of failing are the gauge the relief valve and the feed and backflow preventer. Not a bad idea to replace these while you have the boiler drained for the gauge. So many times after draining to do some service I'd find the feed valve would not open or would not close. Replace that and the relief valve would drip. Aaargh

hot_rod

Gauge no longer accurate

fill valve leaking

Expansion waterlogged or not pre charged accurately, or too small

Indirect coil leaking

Replace or add new gauge

Isolate the fill valve is an easy first test, lower boiler pressure, observe

push in the valve at the bottom of the tank, should be air not water.

109A_5

Multiple issues, bad gauge too.

" it had 13.8 psig so I reduced to 12 psig "

Letting air out probably did not help any, causing less air available to compress as the water expands.