Furnace always building pressure

I would suggest that you install a low water cutoff if you want to keep the fill valve closed. The last thing you want is to get a leak, lose water, and have steam created in your boiler.

whats the harm if the water level drop sand the boiler makes steam? That's what it does in a steam system, no?

e.alleg wrote:whats the harm if the water level drop sand the boiler makes steam?

The resulting explosion is the harm. A steam boiler makes controlled steam. A boiler that runs dry of water can occasionaly either blow apart and kill all occupants, or start a fire and kill all occupants. A low water cut off is mandatory in some states, and should be in all states. It's just one extra layer of safety that isn't all that expensive.

question ;; do the steam boilers currently being mfged. to be fired w/coal , have fusible plugs ?????

The same boiler that is used for hot water heat is also used for steam heat. The only difference are the controls. A steam boiler uses a Pressuretrol, which works at about 1 1/2# of steam. The pressure relief valve is 15#. Those are the two big differences.

Fusible plugs are not used on efm's steam boiler because it has electrical controls. They are, however, used as the high limit safety device on the hand-fired wood/coal boilers.

The 520 steel boiler would be an unlikely candidate to blow up because of its construction, but a cast iron boiler would be.

There was an explosion at a church about 10 years ago in our town. It was a combination of a failed pressure relief valve, a failed low-water cutoff and an aquastat that didn't shut down a runaway boiler. I forget all the details, but the steam blew apart the boiler and took out most of the center of the church, up to and including the roof. This was a large brick structure with a slate roof.

Just to put in my two cents on this issue.....My 520 was constantly building pressure and blowing the prv at 30# as designed.....I had a bad xtrol 30 expansion tank......The bladder must have failed inside.....A quick test is when the tank is hanging vertically tap on the side of it.....The bottom should sound hollow and toward the top of the tank (where the inlet is) should sound solid.....Because water should be in the top half and air in bottom with bladder inbetween....Mine sounded reversed when I tapped on it ( solid on the bottom and hollow up top) so I changed it out and its running between 12 and 17 lbs. constantly now and I'm nice and toasty warm!!

Try this. Close off the water feed and domestic coil inlet valves after you've drained the pressure off to12#. This will rule out a leaking hand valve.

I went over this with some guys today and they brought that up. Otherwise, there is nothing else that can be causing this problem.

97 posts and the damned thing still is building pressure? Something is leaking by; there aren't but 3 sources of supply.....unless some pipe monkey has a flying half-hitch somewhere hidden from view.
It seems that you have replaced the obvious, so unless one of those items is defective (possible) then a gate or stop and waste valve is bad or the coil has a tiny pinhole. There just aren't any other possibilities. Is the C-4 still available?

The best solution is to replace it with a REAL furnace and eliminate the boiler altogether!!!!!!!!!!!!!!!!!!!!!
(You know I can't let go of the furnace/boiler distinction, can I?!) Electric Boiler Man....has a ring to it.....and it's truly self explanatory! Sesame Street could have a special episode brought to you by the letters: E, B, and M!! You must have learned 'agua' means water from your early years, and I still don't know what 'furnace' is in Spanish so you can safely eliminate the "F".

Have you asked anyone local from the forum to just take a look to see if you are missing something.
Up in Maine, they sometimes can't seem to see the forest, the damned trees are frequently in the way. Get the point?
I'm not picking on Maine, guys, it's just that Stoker Scott has taken it in the shorts so much from me, that I'm leaving NY alone until the wounds heal.
Scott was over in Bellows Falls this past weekend for more of the 'special salve', so he sure must be doing better. Hope so.