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[jpand]

I have an old Kerr Titan 101 indoor wood boiler.  The Kerr is tee'd into a System 2000 oil boiler and I have run the system as plumbed with no problem for years.  I am having continuous problems this year with the pressure at the boiler building up to over 30psi, releasing the relief valve, when the temp is running at normal (right around 180F).  At the same time this is happening, the pressure downstream at the System 2000 is only 20psi and the temp is the same 180F.  The only components between the Kerr gauge and the other gauge are the dump aquastat, a flowcheck, and a hand valve.  All of this tells me that there is a constriction somewhere between the two gauges, but I could be wrong.  Sometimes the pressure drops back below 30psi on its own, and sometimes I seem to have success reducing the pressure by quickly closing and opening the hand valve, which I interpreted as clearing whatever was causing the constriction.  I also took out the plug in the flocheck to see if I could identify blockage there, but it seems fine as far as I can tell.  The last thing I did was loosen the thumbscrew on the flocheck to hold it open.  I tried to attach pictures of each gauge and component. but the site is not allowing it.  Any ideas on what the problem could be and/or how to fix it would be appreciated.

It also looks like the feedwater make-up regulator is running normally, as the 30psi relief right downstream  of that is not releasing, and when I closed the shutoff valve for the feedwater it did not affect the pressure.

[Sprinter]

if this is a closed system, then i would look at the expansion tank being bad, the PRV also being bad. cold start it should be 12-16psi , and at 180 about 20-25 psi. if the relief is on the low side of the circulator it might never see high pressure. and vice versa for the outlet or hi side of the circ. blleed off some water down to 12-15psi and see if it comes back up.

[LittleJohn]

A difference in pressure at the same elevation, typically means gauges are on either side of the pump.  I have seen on some commercial jobs were they are pulling 10-15 psi across a pump; and people wonder why cavitation can happen.  Difference in pressure is typically caused by either elevation change or the addition of pressure such as a pump; restrictions in pipe usually cause difference in flow not pressure.

Would also agree with sprinter, check the expansion tank.

Does the system still WORK, or did you notice something major happen before this pressure difference business.

[Sprinter]

 

[LittleJohn]

Jpand, any luck with your system or checking the expansion tanks. 

What is the autofill set at, and what pressure do you typically run the system at???

[MattyNH]

My best advice is replace the relief valve.. Once they are gone.. They are gone.. They will either have a constant drip or pop for no reason.. Shouldn't have anything to do with expansion tank.. Pressurized owb owner here

[Sprinter]

Huh? ,,,,  ok.
By closing the valve he dead headed the circ, which will show a psi change. There's no restriction. When a circulator runs, it does NOT pump water, it circulates it by creating a pressure differential on either side of the circ.    The laws of physics require a fluid to balance this difference in pressure. So the low pressure side chases the high side creating flow. This also could be the reason for the different psi readings.

Now, when an expansion tank goes bad, there is no place for hot water to expand into, from idle to limit can be upto 100 degrees and depending on volume, mine goes from 14-22psi. At a cold start before pressure builds , if the make up water is seeing the low pressure side of the circ it will add water. ( because the failed exp tank didn't maintain system press balance). Now when the system gets up to temp and increased pressure the relief will pop or drip.  Another sign of fail Xtank is sudden air vent leaks, pipe creaking from expansion, or more than normal. Circ flange gasket leaks, Backflow preventer leak on the make up water.
You'll hear the term, "pumping away" in boiler design material. This is one of the reasons you want your make up water connection in the "zone of no pressure change" , cuz even with a good Xtank and large enuff circ it can still happen during starts and stops of fluid flow.

If the relief is more than 4 years old , its preventative maintenance to replace a $12 part.