Water-logged Expansion Tank??


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Old 08-13-06, 05:44 PM
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Water-logged Expansion Tank??

I have on oil-fired hot water baseboard system. A week ago we had a power outage that lasted about 7 hours. Ever since the power came back on the safety blow-off valve on the boiler has been leaking water. I manually operated the valve to see if some rust or scale had gotten lodged in the valve. A modest amount of crud came out but the valve is still leaking. I believe the valve is not that old--maybe 5 years. I notice that the system pressure is only about 10 pounds. When I tap the expansion tank it sounds pretty dead. But I'm not sure how to verify the tank is water-logged. Could a water-logged expansion tank cause the safety valve to leak water? How do I tell if the expansion tank is water-logged? If the expansion tank is not causing my problem what else might be? Many thanks to anyone who's not on summer vacation!!
 
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Old 08-13-06, 06:35 PM
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Expansion tank

Presuming this to be a bladder type tank with an air valve on it. To properly check it you need either to isolate it via a valve, if you are lucky enough to have one between the tank & the system, remove the tank & check the air pressure OR drop the system pressure to zero & check the tank pressure. If when you depress the schrader momentarily you get water, that's a dead give away the bladder is bad.
 
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Old 08-14-06, 06:18 AM
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Water-logged Expansion Tank

Yes, this is a bladder type tank with a Schraeder valve (it's an Extrol 30). It does not have a valve that would allow me to isolate the tank from the rest of the system. I didn't have time to drop the system pressure and check the tank pressure this morning, but can do that this evening. I'm guessing that when I operate that Schraeder valve for the first time in its life it will not seal properly, either! I think I'll just buy a new tank.

Is there anything other than a faulty safety valve or waterlogged pressure tank that would cause water to constantly drip from the safety valve? And why would the boiler being without power for 7 hours bring this problem on? Is there a clue lurking there?

Also, for the past several months I have noticed a whistling noise when the boiler runs (we have a tankless coil for domestic hot water). The noise is most noticeable upstairs, not down by the boiler itself. It does not appear to be related to the motor/pump/fan at all. Could this somehow be related? Or have the spirits taken over my boiler?
 
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Old 08-14-06, 06:28 AM
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Relief valve

Something you can do without having to drop the pressure is to verify the accuracy of the gauge. This is done by checking the pressure at the tank with a tire gauge. If the tire gauge agrees with the boiler gauge, chances are the relief valve is bad. Why it happened after a power outage? Hard to tell.
 
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Old 08-14-06, 08:18 AM
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System Pressure Test

Checking the pressure using the Schraeder valve on the tank would certainly be quick enough. If the valve does decide to leak will the plastic cap that is attached to the Schraeder valve prevent further leaking until I get a new tank?

The boiler gauge pressure is lower than I'm accustomed to seeing. It usually runs more like 15-20 pounds, and now it's a steady 10. Would that tend to indicate a failed expansion tank?
 
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Old 08-14-06, 08:59 AM
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Pressure

The plastic cap should hold if the schrader leaks but they usually don't. The reduced pressure could be an indication of a bad tank but usually we see higher than normal pressures. If the pressure goes up & the relief valve opens more as the boiler heats, it is a good indicator of a bad tank.
 
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Old 08-14-06, 09:39 AM
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Pressure

What you say about increasing discharge from the relief valve as the boiler runs would make sense if the tank was not able to absorb the increased pressure that comes with a higher temperature. I don't seem to see that. I've watched the boiler as the burner runs and the gauge pressure stays pretty constant at about 10 psi and the drip rate from the relief valve also stays pretty constant. It's just a steady drip at the rate of one drop every few seconds. It fills a quart container in about an hour. I'm beginning to think maybe my relief valve is the root of my problems here. I originally suspected the tank because when I tap down along the side it sounds pretty dead except towards the bottom of the tank. I will check the pressure on the tank valve tonight.
 
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Old 08-14-06, 05:59 PM
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If the top sounds "dead" or dull, that's your water. The bottom should ring "dry", which is the air. Given that it sounds like you have a 30# relief dripping at 10psig constant system pressure running/off/etc, my guess is the pressure relief valve is bad.
 
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Old 08-14-06, 06:37 PM
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The safety/relief valve is relatively inexpensive. I strongly recommend that it simply be replaced as a matter of course every three to five years.

It should also be "exercised" at least once every year by pulliing the handle and allowing a good blow. It is best to do this in the spring in case it does not properly reseat you can then shut the system down to replace the valve.

If you have separate thermometer and pressure gauge then also replace the pressure gauge, it is not too expensive. If you have a combined pressure/temperature indicator then it will cost a bit more but I still recommend replacing it every five years or so, it is cheaper than having it calibrated.

Don't forget to check your "automatic make-up water valve" which is just a pressure reducing valve to maintain about 10-12 psi on the system when it is cold.
 
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Old 08-17-06, 08:27 AM
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And the answer is....

....the pressure relief valve was definitely bad. And the expansion tank had not completely failed but it certainly had a lot of water in it when it was removed. So I changed the both of them. Usually these fail on some wicked cold night in the middle of the winter so maybe my luck is changing a bit here.

Thanks to all for your help and advice on this. It's good to know all you heating system gurus still watch this forum even when it's not heating season.
 
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Old 08-17-06, 05:04 PM
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Thumbs up Fixed

Wise move & one less thing to worry about. Done & over with especially since you had to drop the pressure to change the relief valve. Way to go.
Should the need arise, we're here & glad to help when we can.
 
 

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