Help With Boiler Pressure !

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Old 02-08-07, 06:06 AM
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Unhappy Help With Boiler Pressure !

I live in the U.S. I have a very simple small old gas hot water heating boiler in my home. (BRYANT model: 234-3GW series C). It heats the house nicely. The boiler temperature stays between 135-140 degrees which is okay. No problem with that. THE BOILER IS NOT OVERHEATING. However, lately I've noticed problems with the pressure. Maybe this has been happening for years and I just have not noticed it. I don't go into the basement often. The problem is this. Whenever the weather temperature outside falls from about the 40's (or above) down in to the 20's (or below) the pressure gauge rises past the 30 pound limit such that it pops the relief valve. THE BOILER TEMPERATURE STAYS STEADY HOWEVER AND DOES NOT OVER HEAT (135-140 degrees or there-abouts). This happens a few times intermittently (spilling some water each time which is replaced by the automatic fill valve) and dropping the pressure each time to about 14-20 lbs. (which is good) until the system somehow stabilizes and STOPS doing this for some reason. This cycle will not happen again until the outside weather temperature rises high enough then falls low enough again. I'm stumped. I believe the expansion tank is working okay because when I knock on it it sounds very hollow and empty but maybe not. But I don't know how expansion tanks work so I'm not sure. Please help. I do not have a valve between the boiler and tank. My fill valve is a Thrush No. 6F P.R.V. Model C 70. It is green with a thumb screw on top. I fiddled with the thumb screw and manufacturer's web site says that counter-clockwise is to factory setting (12 lbs. out 45 lbs. in) and clockwise is fast fill. I have the thumbscrew turned all the way counter-clockwise NOW. I don't know where it was originally set. PLEASE ADVISE HOW TO SET THIS THUMBSCREW SETTING. Does this thing have air purge? How does that work? I know it contains a check valve too. HELP. Also, my expansion tank is an old one. It's a big black cylinder hung up to the rafters. It is not a newer diaphragm one. There is no circulation pump. It is all gravity. I have a small two story house. Cast iron radiators. Works very well except for this weather/pressure/pop-off problem. Seems the pressure sometimes goes all over the map. I bled the radiators too. I don't think it used to pop off the relief valve before.
 
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Old 02-08-07, 09:38 AM
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You need to drain that expansion tank. You might also want to think about replacing it with the modern style ones, that keep the air in them longer (although when the do leak, then the new ones are disposable, but they work better while in operation).

If you are sure that you know how to add water back to the system you can do as follows.

Shut off the boiler.

Shut off the valve where the boiler system gets it's water from the house system -- the "water feed".

Follow the piping from the expansion tank to the boiler and close the first valve.

Then connect a hose to the drain on the overhead expansion tank if you need it or you can just let it splash if it's an open area near a drain and there's nothing that can get wet.

Then open the drain and let the tank drain completely. If you don't remove all the water, you'll have a partial vacuum in there.

One drained completely, close the drain to the tank.

Then open the water feed valve.

Then... very slowly open the valve between the tank and the boiler. This will bring water very slowly into your system.

Once you're pressure is back to 12 or 15psi, whatever the norm is and you can't hear water gently going into the tank, open that valve all the way.

If you have a Low Water Cut Off protection device, then shut your water feed off.

Repeat every time the pressure starts going through the mid-20s, until you get a diaphram tank... ;-)
 
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Old 02-08-07, 07:21 PM
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Unhappy RE: Help With Boiler Pressure

But I don't have a valve between the big black expansion tank cylinder and the boiler. Zip. Nada. So what else can I do? Also the expansion tank sounds hollow and empty when I knock on it but maybe it is deceiving and is really full. Also, how do I set that thumb screw on the Pressure Reducing Valve properly. It is wound all the way out counter-clockwise. Exactly how does that thing work? When I close the feed valve from the house water then pop the lever on the relief valve for an instant (once the system is all fired up on a very cold night) the pressure in the system falls way down to almost zero. Then when I slowly re-open the house water feed valve the pressure slowly comes up to 10-12 pounds and then I close the house water feed valve again. That seems to be temporarily working until the weather temperature outside goes way up into the 40's then the problem starts again at night when the outside weather temp. falls back down into the teens and the pressure rises. But I don't think the pressure reducing valve would automatically stop feeding at 12 pounds on its own. I think it is messed up or the thumbscrew is set wrong.
 
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Old 02-08-07, 09:29 PM
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If your feed needs to be on, get help right away, because it's leaking.
 
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