Lost system pressure, boiler shut down.

Jimbo_5

Just experienced an unusual boiler shut down. Woke up to no hot water in the shower. When down to the basement and found the boiler (Triangle Tube Prestige 110) trying to fire. Looking around I noticed the gauge on the supply line was at 0 psi, rather than its usual 14 psi.

After looking around finding no obvious water leaks or signs of leakage, I opened the closed makeup water valve. You know how slowly they fill, yet in seconds the gauge was back at 14 psi. I closed the valve again and fired up the boiler. It has been running fine ever since. The boiler was installed 12 years ago, has 2" supply and return black iron pipes from an old gravity system circling the basement feeding 9 cast iron radiators and 2 rooms of ci baseboard on 2 floors. It also heats a Triangle Tube indirect 30-gal hot water tank. This problem has never happened before. Two years ago the expansion tank failed for reasons unknown. Replaced it and all was fine.

I cannot figure out what might have caused this to happen. Any ideas? Perhaps the Spirovent eliminated some trapped air? Thanks in advance for any help.

mattmia2

How often did you check the pressure? It could lose enough water to get to 0 psig through minor seepage at valve packings and such over months or years. If it only needed to replace essentially the water beginning to compress the diaphragm in the expansion tank then it wouldn't take much to replace that water. You should check it when the whole system is at temp to make sure it doesn't go up too much and the expansion tank is doing its job and you should check it again cold if the boiler was hot when you filled it because it will go down when the boiler cools if you have the auto feed closed.

EBEBRATT-Ed

@Jimbo_5

If you only added a little water and the gauge jumped up quickly it is probably an expansion tank issue

Solid_Fuel_Man

How long since the air pressure in the expansion tank was checked? You need to bleed to system to 0 psi and set the air pressure to 12 psi if you are running a 14 psi system. You likely have two ex60 tr anks if it was a gravity system. Very large volume of water comparatively speaking. 

psb75

It also could have been just an air-lock situation. Interesting that you operate the system with autofeed valve shut off. Maybe leave it open? I daresay most ARE operated with valve left open. You CAN operate it with the valve closed, but either YOU or a device has to monitor the fill-status/pressure of the system then.

Ironman

In an old system like that there can be some very small leaks, usually the packings on radiator valves, that are almost unnoticeable.

There was a long discussion on here a few years ago about leaving the fill line open or closed. I think the best advice was to leave it slightly cracked open to maintain pressure on the system. That way, if there was a catastrophic leak, the fill line would only provide a small steam of water instead of full blast.

A Caleffi fill valve has a knob where you can throttle the flow down once the system is filled.

mattmia2

Ironman said:

A Caleffi fill valve has a knob where you can throttle the flow down once the system is filled.

Oh, is that how that is supposed to work? I wasn't clear from the instructions that the knob could be used to throttle the flow.