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Thread: Water coming out of overflow on boiler....

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    DIYourselfer is offline New Member
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    Water coming out of overflow on boiler....

    I have a Peerless boiler MCB-097. Its about 15 years old and today for the first time about 2 gallons of water came out of the overflow valve into a bucket.
    The valve is set for 30psi and when I turned on the heat to test it the internal water temp went from 170 to 210 and the pressure went from 12 psi to about 29psi and thats when the water started to come out of the valve.
    The expansion take is the old style. It looks like a mini 55 gallon drum located above the boiler attached to the ceiling. I assume the issue might be that the tank needs to be drained. Is this correct?
    The water line in to the tank has a valve to turn the water off so it can't flow into the tank and then their is a drain valve on the other end. What is the procedure to drain this tank? Do I turn off the intake and just open the drain? Do I do it when the water is hot or cold?
    Thanks in advance,
    Joe

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    AmeriServ is offline New Member
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    The boiler should not go to 210 Deg F. The temperature should not go much higher than 210 because the water will turn into steam and then you have essentially a potential bomb without the pressure relief valve.

    Too many things to discuss here, first did you manually turn on the heat by overriding any limits or safeties, if so then you are more than likely ok as far as controls are concerned. If not then you may have a serious problem on your hands. The temperature control should not have allowed the temperature to go that high unless you have it set that high and there should be high limit to back up the temperature control set at around 200 and this should have shut it off also.

    The pressure/temperature relief valve is doing it's job properly.
    having said that there is several things that can affect the pressure in the boiler.
    The first is the obvious one and that is the higher the temperature the higher the pressure as I had indicated above 210 deg F is too high and too close to steam.

    The second is that you need to start at reasonable pressure to begin with, for instance, you have a cold water make up regulator that makes up water to maintain the pressure in the hot water pipe loop and subsequently the water in the boiler also. If this regulator is set too high or the spring has failed and the water gets cold normally the pressure will drop also and the regulator will add some water to get it to the set pressure on the regulator. Then when the water heats up the pressure gets too high. I have seen more water make regulators go bad than expansion tanks and they will make up too much water causing high pressure problems.

    The third and last thing to check after everything above has been checked, including the temperature controls and safeties is the expansion tank.
    There are two types of expansion tanks. A Diaphragm Tank or sometimes called a bladder tank and these are filled with compressed air or a steel holding tank, which traps air in the top half. The diaphragm tank is charged with air to the operating pressure of the boiler set by the regulating make up valve. Never release or add air to the diaphragm tank when it is till connected the boiler system. Tap on the tank and it should sound hollow through out. If the bladder has leaked the tank will completely fill with water and if not properly charged with air it will fill 1/2 way with water.

    For the steel holding tanks there is sometimes a sight glass on the front of the tank to see the water level in the tank. The tank should be around half full. If the tank is filled near the top or completely filled you will need to drain some water. Turn the boiler off and close the valve that connects the expansion tank to the boiler and open the drain valve. Drain the tank until it is empty. Close the drain valve and the re-open the valve to the boiler. The expansion tank should filled to the half way mark or less and trap air in the top of the tank but if the tank fills again after a few days then there is a possibly a leak in your tank.

    No residential boiler should ever have to heat water to 210 Deg F, 180 is about the maximum I have generally set commercial systems and that is during the coldest of winter months on old systems.
    Last edited by AmeriServ; 03-03-2008 at 06:19 PM.

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    DIYourselfer is offline New Member
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    Well I drained the tank till it was empty then I turned on the heat and watched the gauges. The psi was steady at about 12psi and the temp went from 120 to 210 which seems high to me. What should the normal temp and pressure be???


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    AmeriServ is offline New Member
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    That depends on your home and the system. Again 180 should be your maximum, or as high as it ever needs to get. Anywhere between 130 and 180 should be your set point depending onhow your system performs and heats the house.

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    DIYourselfer is offline New Member
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    Thanks. I just need to set the hi temp lower now.

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    DIYourselfer is offline New Member
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    I need 5 posts to post a link so the next post will have a link and a question.

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    DIYourselfer is offline New Member
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    I shut off the power to the boiler and took the cover off the relay box so I could turn the hi temp limit which is set at 190 down to about 160.
    Here is a picture of the limiter:

    http://s251.photobucket.com/albums/g...=IMG_0013a.jpg


    http://s251.photobucket.com/albums/g...=IMG_0010a.jpg

    I can't seem to move the pointer off 190. Do I push the dial down away from the pointer and then turn the dial to the new setting or do I somehow pull the pointer away from the dial and turn the pointer. I don't want to break anything but I can't get these 2 pieces apart from each other. Any advice?

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    LazyPup's Avatar
    LazyPup is offline Deity
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    While most substances expand when heated and contract when cooled, water has a rather unique property. Water reaches its maximum density of 62.4lbs/cu.ft at 39degF and whenever it is heated or cooled from that temperature it expands until it reaches a maximum expansion of approximate 10% greater than the maximum density. In turn, whether water is in solid, liquid or gaseous form (Ice, water, steam) it is not compressible therefore whenever we design a closed system that contains water we must make allowances for thermal expansion otherwise the water would freeze or expand and rupture the containment vessel. In actual practice we see evidence of the expansion of cooling when a water line freezes and ruptures or the expansion of heating when we get a discharge of water from the T&P valve. On the other hand, if we did not have a T&P valve the expansion would rupture the boiler vessel or break a line.

    The immediate solution to this problem would be to turn the burner off, then close the valve from the boiler to the expansion tank and open the expansion tank drain valve. (Be very careful here because at 170degF the water could cause serious scalding or personal injury). Once the expansion tank is drained you would then close the drain valve, open the boiler to expansion tank line valve and turn the burner on again.

    While this procedure will alleviate the problem, what is more important is to determine what was the initial cause of this problem to prevent it from re-occurring. In general the expansion tank should be drained annually at the start of the heating season however the post makes no mention as to how long it has been since this tank was last drained. Based upon the fact that the homeowner is unsure of the draining procedure it is highly likely that this tank has not been drained for a number of years.

    There are many circumstances that can account for how an expansion tank will become saturated with water. With this type of expansion tank that does not have a bladder there is the potential that some of the air in the expansion tank will be absorbed into the water. As the air is absorbed into the water it reduces the volume of air in the tank and the automatic feed water valve will allow additional water into the system. The annual draining as mentioned before normally controls this condition. If the system requires draining the tank more than once per annum we must then consider other root causes of the problem.

    First examine the expansion tank carefully, especially the upper 1/3 of the tank that would normally only contain air. If you see any evidence of paint blisters or rusting it is quite possible that the tank has a micro-fine crack that is allowing the air to slowly escape.

    We must also consider the age and condition of the boiler feed water valve. If it is an old valve or if you have a severe hard water condition it is quite possible that mineral scale has built up on the seat of the valve and it is allowing additional water to slowly enter the boiler.

    One condition that generally goes totally unnoticed is water hammer in the house potable water system. When water hammer occurs in the house potable water distribution system the shock of the water hammer is often sufficient to force a minute amount of water past the boiler feed water pressure reducing valve. If this condition persists it will cause the boiler to be overfilled. The solution here is to install an expansion tank on the water heater to control the water hammer.

    In a previous follow up post it was mentioned that operating the boiler at 210degF is dangerous because the water could flash to steam. This simply is not true. Many people make this erroneous assumption based upon the fact that water boils at 212degF, but here again, that is an incomplete statement. Properly stated, Water boils at 212degF at “Standard Atmospheric Pressure at Sea Level which is 14.7psi absolute. In a closed system as the pressure is increased or decreased above or below standard atmospheric pressure there is a proportionate increase or decrease in the boiling temperature of water. By example, if we pull a deep vacuum (29in/hg) the boiling temperature of water is then 40degF. In the refrigeration industry they take advantage of this fact by pulling a deep vacuum on a system prior to charging with refrigerant. When in deep vacuum the structural components of the system contain enough latent heat to boil any residual water that might be present, thus the system is left totally dehydrated prior to charging the refrigerant.

    The gages used to measure pressure in the plumbing and heating industry are calibrated in PSIG (pounds per square in/gage) which means the gage would indicate zero PSI at standard atmospheric pressure and it indicates pressure increase above standard atmosphere.

    The mechanical codes limit unattended heating boilers to a maximum working pressure of 15psig for live steam or 30psig for Hydronic (circulating hot water), which is evidenced by the fact that the Hydronic pressure relief valve is set for 30psig. At 30psig the actual boiling temperature of water is 276degF so you can see that even if you are firing at 210degF it is still a long way from the boiling temperature of the water.

    Due to the sensitive nature of the controls and the extreme potential for danger if the controls are not set correctly absolutely no one except trained professionals should attempt to make any adjustments on boiler operating controls.

    (On a side note, the commercial high pressure boilers used to produce steam for commercial electrical generation fire at 1500psig and at that pressure the boiling temperature of the water is well over 500degF.)
    Last edited by LazyPup; 03-05-2008 at 12:16 PM.

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