Expansion tank or pressure reduser valve Or something else?

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Old 12-19-08, 12:56 AM
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Expansion tank or pressure reduser valve Or something else?

Hi, I'm new to this forum,didn't find answer anywhere,may be someone can help me.
I have an oil boiler for heating and hot water. This year my pressure relief valve started to spit water when boiler is working for heating. Pressure reduser set for 10, bladder expansion tank set for 12. When sistem is cold, pressure is around 10, after firing up it's going up to 30 when working for hot water,and up to 35 when working for heat, and then pressure release valve is leaking/set for 30/ I was thinking it's a pressure reduser,but since cold sistem is OK,may be it's not. Checked the expansion tank,seems like upper half filled with water/sounds like it/ bottom part empty/bladder type/,whole sistem is about 5 years old. I'm thinking now it's a tank, but it's not filled with water completely.sorry for the long post ,but I have more questions more than answers Thank you
 
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Old 12-19-08, 12:44 PM
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Isolate the expansion tank completely (removing it is probably best but be very careful because it may be a full keg of boiler water), and then pressurize it to 12 psi. Let it stand for an hour and see if that changes.

Were it me, I'd simply just go get a new expansion tank, because that is exactly what those symptoms all point to...
 
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Old 12-19-08, 03:29 PM
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Be darn sure to first turn off the make-up water AND turn off the boiler and allow it to cool to no more than 100 degrees BEFORE attempting to remove any piping. Open the boiler drain long enough to reduce the pressure to zero and then close the drain. Only after doing this is it safe to open any piping connections.
 
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Old 12-19-08, 04:12 PM
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After sistem is drained, how to fill it back with water? Any special things to do? Thanks for advise!!!
 
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Old 12-19-08, 04:19 PM
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By the way,is it possible that tank is bad even if its half/hot,half/cold? can I check the pressure with manometer through the air valve and what this pressure gonna tell me?
 
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Old 12-19-08, 04:44 PM
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There is no practical way to determine the condition of a bladder type expansion other than isolating or removing it from the system. Temperature differences and hollow/solid sounds when rapping the side just doesn't work. Testing the air pressure in the bladder when the tank is connected to the system will measure the system pressure, not the bladder pressure.

You don't need to drain the system, just remove the pressure. When you have the system closed up again you open the make-up water valve and allow it to repressurize to the setting of the pressure reducing valve (PRV) usually between 12 and 15 psi. You may need to manually bleed the air from the heaters or you may need to "purge" the entire system if you do not have individual air vents on the heaters.

Some pictures (more is always better) of the boiler and nearby piping may help to explain some of this. To post pictures you need to first upload the pictures to a photo hosting site such as photobucket.com or villagephotos.com. and then post the public URLs for the pictures (or album) here. More pictures are always better than fewer. Please have CLEAR pictures and have both close up pictures and ones from a far enough distance that we can see how the various parts are interconnected.
 
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