Problem with boiler pressure


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Old 12-27-04, 11:40 AM
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Problem with boiler pressure

I just moved into a house with an oil-fired furnace with radiator heat (original to 1925 house). I have a bucket under a pipe which seems to be for when the system has too much pressure. This has filled 2x, and I noticed the pressure creeping into the red zone of 30 psi. So I bled all radiators, then emptied the expansion tank, which dropped it down around 8-10psi cold/18-20psi hot. However, it has come back up around the 30 psi level a few more times. I have emptied the expansion tank 2 or 3 more times, but there must be a larger problem.

My amateur diagnosis is that it's either a broken pressure gauge, or the valve which lets in fresh water is malfunctioning (letting in too much water, so no matter how much I empty the expansion tank, the pressure is too high).

Also - when I empty the expansion tank, should I close the valve that leads to it from the furnance, or keep open while I empty the tank? I thought it was there to close while I empties the tank, but I'm not sure. Is the automatic intake valve set at a certain pressure, and can it be adjusted (if it's putting too much water in the system)?

Lastly, is there a standard level of psi for the system when hot and cold, or does it depend upon size of the house?

Thx

Marc
 
  #2  
Old 12-27-04, 05:50 PM
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Marc,

Excellent problem description. The only thing missing was how many floors in your house.

It sounds like your auto-fill valve is set too high. Trace the piping coming into the boiler, and you should find a valve that looks like a bell, with a stem or thumbwheel coming out of the top of it. Loosen the stem (counter-clockwise) about two full turns. Then go pop the PRV (pressure reducing valve) and let it drain into a bucket. You want to get the pressure down to around 12 - 15 psig if one story house of 15 - 18 psig if two story house. Do all of this with the thermostat turned down, so the circulator is not running.

If you bleed the pressure down to the right range, pay attention to the auto-fill valve that it does not open and add more water. You want to adjust it to keep the pressure in the correct range (above) based on how many floors are in your home.

One final thing, you keep draining the expansion tank. Does it have a bladder? Look for a Schrader valve (like a tire valve) if you find one, check the pressure with a tire guage. It should be set to 12 psig. You may need to use a bicycle tire pump to increase it. If you get water out of the Schrader valve, the bladder is ruptured and you will need to replace the tank.

Good luck and post back if you need more help,
 
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Old 12-28-04, 06:14 AM
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Got it - mine is actually a 3 story house (furnace is in basement, then 2 full floors above this) - what is the correct psi setting? And is this setting for cold or hot - meaning, is this when the system is not running or fired up?

From your instruction, I take it that I should not reduce the pressure by emptying the expansion tank, but rather use the PRV (which empties into a bucket). Is there any danger of emptying the expansion tank? I won't do it again, but that's what I had been doing, and want to understand if that is contributing to the problem.

Regarding the expansion tank, I didn't see any valve other than the one to turn to let water out. How would I determine if there is a bladder? All I see is an inlet pipe from the furnace (with a valve to open/close), and the aforementioned outlet valve. I understand to now use the PRV to reduce pressure in the system, but what then is the purpose of the expansion tank valve? When should this be used?

One last question - given that I've emptied the expansion tank and changed pressure in the system a few times, is there any chance I've re-introduced air into the system, and now I need to re-bleed the radiators? Just trying to think of all possible angles....

Thx

Marc
 
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Old 12-28-04, 07:23 AM
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Marc,

I would call your house a two-story. 15 psig of pressure will raise water 33 feet, so 15 to 18 psig should do fine. Pressure measured with "warm water", e.g. boiler not currently fired and circulator pump not running. Just turn the thermostat down while you adjust boiler pressure.

If you do not see a schrader valve on the expansion tank, then it is not a bladder tank. Yours is probably a long narrow cylinder hung horizontally between the rafters above the boiler. Emptying the tank did not harm anything, it needs to be full of air when you first bring the boiler up to pressure. It is there to allow a place for the water to expand, when the boiler fires. The water in your system will expand about 5% between low and high temperatures. The expansion tank acts as a "bulge in the pipeline" to allow the water to expand by compressing the air in the expansion tank.

Every time you add make-up water, thru the auto-fill valve, you introduce some air to the system. Domestic water contains some dissolved and entrained air, that is released when it is heated. Best way to check is to go to the radiator that is furthest and highest in the system and bleed it. Air will always migrate to the highest point. If you have to do a lot of bleeding, go back and check the boiler pressure, 'cause you are venting boiler pressure when you bleed the radiators. A very small amount, unless you bleed a lot of air.
 
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Old 12-28-04, 07:50 AM
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Thanks a bunch - I will try this when I go home tonight. I appreciate your help.

Marc
 
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Old 12-29-04, 08:04 AM
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Well, I tried this last night, and although the pressure went down to around 17 psig, I could not adjust the auto-fill valve. Mine doesn't really look like a bell - it has a thumb-screw coming out of it. But when I turn it, it is incredibly loose - I feel when I turn it, I'm not really catching anything in this valve. It feels as if it's loosened way too much. I'm not sure if I'm setting this correctly, or if it is working. I checked this morning, and the pressure is back at 30 psig.

Also, I'm concerned about my PRV - when I popped it, it reduced the pressure to about 21 psig. It let out water for about 20 seconds, then stopped - very normal. Then I hit it again so I could get into the 17/18 psig range. This time, after the initial heavy flow (which immediately reduced the pressure to the desired range), it proceeded to trickle out a very small amount of water for 30 minutes. This extended slow release barely moved the pressure needle, but I started getting extremely nervous that it wouldn't stop, as I had to constantly monitor it and empty about 10 buckets of water. I fiddled with the PRV a few times, until it eventually did stop. Is there something wrong with my PRV?

I think it may be time to call in a professional....

Marc
 
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Old 12-29-04, 02:34 PM
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Wink

I think you should get a new auto fill and PRV they come as a set like the PRV will go off at 30 psi the auto fill will be set at 15 psi you will have to kick that up to the 18psi like said to get to the 2nd floor. Make sure that the expansion tank is drained of all water when you go to refill the system.

Ed
 
 

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