boiler pressure on the rise

[ssupercoolss]

just before the end of the season last year, i switched my wood boiler to a parallel install instead of the series hook up, that i originally did. with just a few burns under my belt this year, it seems as though i am experiencing a pressure rise that i never saw when this was in series with the oil boiler. i keep looking at the expansion tank for the cause of this, but just dont know whats going on inside that thing. it seems as though the expansion tank on the oil boiler was working properly and maintainig the proper pressure on the system. now that i have cut the oil boiler out of the equation, i have this pressure issue. to me, it appears as though there is never any water in the exp tank. it is located under my air scoop, before the circulator, its a diaphram type, i think its 4.4 gallons. i just took the tire gauge to it and it says 12 lbs. but is it actually charged, or is it low and just reading the static pressure on the boiler? do i need to depressurize my system to check the charge on the exp tank?

thoughts?

edit - boiler pressure starts out at about 12 psi when cold, and makes its way up to 20 psi when hot.

 

[ohbie1]

I have a couple of ideas to look at:

The boiler pressure does rise some as the water heats up.

The exp. tank could be water logged. Just poke the air valve quickly, if
you get a spirt of air (OK), but if you get air+water it's shot. (This test does assume your exp. tank is installed rightside up, meaning the air valve is on the bottom)


Since I'm guessing you added some 40 gal. or more (the water content of your wood boiler), you shold have a second exp.tank to handle the extra water expansion from those additional gallons.

 

[ssupercoolss]

the exp tank did have air in it, it was a little on the low side so i bumped it up. each system has its own exp tank. 1 on the oil side, 1 on the wood side.

 

[ohbie1]

the exp tank did have air in it, it was a little on the low side so i bumped it up. each system has its own exp tank. 1 on the oil side, 1 on the wood side.

I can think of only three more possible problems:

Is the wood boiler's exp tank the right size? I know my wood boiler's exp tank is 2-3 times the size of my OB's.

When the boilers' water cools down......Does the pressure drop back to 12psi? If not, the pressure reducer on your fill valve (from the domestic water) is either shot or the fill valve is on fill (instead of auto.)

Maybe you have an air pocket in the sys., and that air is expanding to cause pressure??

 

[ssupercoolss]

i thought i sized it right, but maybe i need to take a second look at it. when i first put this all together in series with my OB, i didnt really have going parallel in mind, so maybe i goofed up there.

pressure does drop back down to 12 when cold, and i have even run it with the make up water shut off, so i should actually have that ruled out.

there is a very good possibility i am chasing around some air. i bled my radiators the other night, and much to my suprise i got quite a bit of air out of them.

thanks for you help, by the way.

 

[ohbie1]

In case it helps:

I followed Tarm's recommendations for WB exp tank. They said to use an Amtrol #60. This is suitable for up to 86 gal. My WB is around 45 gal., and then you have to add in the additional volume from all the plumbing.

This exp tank is 22" tip to tip whereas the OB exp tank is about 11" tip to tip.


Good luck!

 

[ssupercoolss]

once i get some colder temps i will fire it up again, and check things out once again, bleed the radiators......i think the bleeding of the radiators help take the pressure down a bit.

 

[twofer]

I had a similar problem this season when I fired up my system. When I isolated and disconnected my expansion tank I found that over the summer it had lost some air pressure and thus was limiting the amount of water expansion it would accept.