boiler press. goes up and down with temp

mark schofield

I had the same problem/symptoms. In my case the Extrol tank diaphram was leaking so the tank was waterlogged, and I'd get 15 psi difference between low and high limit. Checked the charge and water dripped out of the tank. A new tank solved the problem in my case. Now about a 5 psi difference. Mark S.

Mike L

press change as temp rises and falls

I'm working on a 4 section Burnham(v-84)with three 007 piped on the return,prv piped into the extrol tank(#30) as the boiler temp increases so does the pressure.Every now and then the relief will blow off.there are some supply water issues,PH Hardness ETC.I pulled the system apart looking for dirty im.wells bad gauges bad compression tank,plugged tee from prv.bad feeder valve ETC.because as the temp falls so does the press.but the prv will not bring it back up.Good thing I suppose or the relief would be going off all the time.The boiler gauge was all plugged up and the immersion well was dirty. New gauge, clean well,cold boiler at 10 psi,the boiler no longer overheats but you can watch the press. rise to 25 psi on a call for heat and drop to 5psi if you cool the system down below low limit to say 100 deg. I can't belive that the #30 is to small. am I wrong? If I'm not wrong I'm stumped as to what is wrong other than a design issue. By the way I did not install this job I inherited it,I did clean out the system and corrected the PH but the problem is still there. What next?
Brad- Bruce thanks
I reduced the tank charge a little, to app. 9psi figureing it might hold more water and that seemed to help some but still did not fix the problem. And no this is not a gravity conversion, it's new construction 4 yrs old. pumps on the return.I suspect it's a tank vol.issue just seems like I've had larger jobs with the same size tank that worked fine, however after fixing the overheating issue the relief has not gone off.

Brad White_141

Not enough

expansion tank capacity I suspect. Is this an older converted gravity HW system? All of that volume adds up. A #30 is really not that big. Buy it a twin sister and pair them to the same connection.

But also, are you pumping away? Separate question/issue.

But the pressure issue I think is that simple. More tank.

brucewo1b

Make sure you have the correct charge

in the tank, 12PSI with no presssure on the system otherwise it will do as your saying or else its not enough tank for the system as Brad said. The only other thing I have seen was the tank on the wrong side of a check vale and it would increase in pressure and blow the relief valve.

adambuild

?

12# is only good for 2 stories, 19# for three.

brucewo1b

Mike

You want the same air charge in the bladder as you have on the system ie what ever the Pressure reducing valve is set to, as Adam said 12 PSI good for two stories and 19 for three. Now if the pump is pumping toward the expansion tank you might be adding pressure to the relief valve, if pumping away from the expasion tank you should be ok at that point. Where is the expansion tank located?? on supply piped with the Pressure Reducing valve or somewhere else??

rumn8r

Speaking technically...

you need 1/2 PSI of fill pressure for each foot of vertical heighth above the boilers pressure gauge, PLUS 5 PSI to avoid the possibility of flashing to steam at the top of the system.

19 - 5 = 14, 14 X 2 = 28' of altitude. Assuming each floor is 10 foot tall, you're just shy of whats needed, however, if the boiler is in the basement, and its 4 or 5 foot tall, and you have 3 stories above that with baseboard convectors, that would equal roughly 25 feet, which would only require 12 PSI plus 5, would equal 17 PSI, so you'd be OK with 19 PSI. Now if the third floor is served by ceiling mounted fan coil units, then you have to account for the additional rise in elevation...

Make sense?

ME