Pressure build up in base board hot water

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Old 10-25-16, 07:49 AM
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Pressure build up in base board hot water

The system is about 15 years old.The water pressure before turning boiler on is about 8-10. After the boiler is on the pressure goes up to about 35,it takes about 20 minutes. The emergency water release valve does NOT open at all. No water is going out of that valve. I have heat (pipes are warm) in the pipes leaving the pumps and going back into the boiler. The pressure in the expansion tank is about 16.
 
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Old 10-25-16, 07:56 AM
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The most likely cause is the expansion tank. You probably have gauge problems as well and perhaps even a stuck boiler safety valve.

Please take several pictures of the installation and post them, preferably high def pictures hosted on a site other than the forum. Do not use tinypic. Pictures need to be WELL LIT AND IN FOCUS or they are useless. I do NOT need close-ups of anything at this point but DO need to see how the various parts are connected.

Does your boiler also supply domestic hot water and if yes, is it via a tankless coil (internal to the boiler) or a separate water heating and storage tank?
 
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Old 10-25-16, 02:42 PM
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The boiler does NOT supply domestic hot water. The boiler safety valve has been opened a few times and water did come out. Even with 1-2 pounds of water pressure the pressure rose to almost 30 pounds with boiler running. Waiting for pictures from my son. After running for about 20 minutes the pipes on return for 3 zones are hot.Close inlet water supply and pressure still went up to about 30.
 
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Old 10-26-16, 03:25 AM
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You have to have the system pressure at zero to check the pressure in the expansion tank. There's a sticky at the top of the forum page with some info. Good luck, Steve
PS- listen to what Furd tells you. He knows what he's talking about
 
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Old 10-26-16, 11:26 AM
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I changed the Expansion tank,not sure if bad but was a little old. I had brand new in by bsmt,a few years old,never used.We then put another pressure gauge on and there was about a 10 pound difference between both of them.I went to store and picked up new pressure/temp gauge and it works fine as of now. Tomorrow is another story.Thanks for the time.
 
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Old 10-26-16, 11:42 AM
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As Steve mentioned, you MUST have the system pressure at zero to check the air cushion in the expansion tank UNLESS you have valving that allows you to isolate the tank from the system. Be wary of using a pencil-style tire pressure gauge for this as they are not all that accurate. A high quality dial-type gauge with a maximum reading of 30 psi connected to a tire chuck is ideal. Do not drop or manhandle the gauge as they are easily knocked out of calibration. Also, a tire gauge of any kind that has a top reading of 100 psi or more is pretty much useless for measuring what is normally a 12 psi pre-charge.

It is a good idea to change the boiler safety valve every five years.
 
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