Pressure will not hold at 12# in my boiler..

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Old 08-04-18, 04:52 AM
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Pressure will not hold at 12# in my boiler..

My boiler pressure gauge keeps reading 25-30# all the time. I replaced the pressure reducing valve but it'll still peak at 30#. I'll drain the system down to 12# and the next day it high again.
 
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Old 08-04-18, 06:41 AM
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Your expansion tank may waterlogged. Depressurize the system and check the pressure in the expansion tank with a tire gauge. Pump it up to 12 psi with a bicycle tire pump, and then re-pressurize the system by lifting the bail on the pressure reducing valve. Let us know how you do.
 
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Old 08-04-18, 12:48 PM
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Do youbhave a domestic water heating coil in your boiler? It may be leaking.
Or your boiler feed may be failing.
Sid
 
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Old 08-05-18, 01:13 AM
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Classic Problem and Solution

From old NJT post:
The majority of boiler pressure gauges are defective or inaccurate.
When dealing with boiler pressure problems, the FIRST thing that must be done is to verify the accuracy of the pressure gauge. A test gauge is easy to construct.
https://www.doityourself.com/forum/b...ure-gauge.html

I also recommend using a longer hose so gauge can be positioned to read easily when working on system. A clothes washer hot or cold water supply hose is good. It is good practice to flush debris from faucet before connecting temp gauge.
 

Last edited by doughess; 08-05-18 at 01:28 AM. Reason: c
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Old 08-05-18, 10:39 AM
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Do I have to take off the tank or just depressurize it?
 
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Old 08-05-18, 10:41 AM
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After system pressurizes to the +/- 12psi...... turn the water fill supply off and see what happens.

Depressurize the system. Te tank can remain installed.
 
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Old 08-05-18, 01:23 PM
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My expansion tank only had 5# in it. I put 12# of air in it and pressurized the boiler, my pressure gauge is holding at a little over 12# at the moment. I'll have to run the boiler, that's usually when the pressure will rise, I'll let you know, thanks...
 
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Old 08-05-18, 04:40 PM
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Boiler ran a little bit, pressure went up to 15#, I'll keep an eye on it. It's a brand new pressure reducing valve on the boiler, you think it was set wrong at the factory? Next should I try backing out the adjusting screw and see if that will lower the pressure?
 
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Old 08-05-18, 04:48 PM
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No, wait. Everything sounds normal, so far.
 
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Old 08-05-18, 04:53 PM
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Let the boiler come to full heat and then see what the pressure is.
It's not un-common to rise 5-10 degrees during heating.
 
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Old 08-05-18, 04:56 PM
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15 psi is fine. Relax. Take two aspirins and call tomorrow morning or Tuesday morning.
 
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Old 08-06-18, 05:32 AM
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Adding air to the expansion tank greatly improved if not completely fixed the situation.

With 5 PSI in the expansion tank with the rest of the system depressurized, once you opened the fill valve to restore the proper amount (quantity) of water to the system, water rushed into the tank to squeeze the remaining air inside and make the pressure everywhere in the system including in the expansion tank approximately the same. (Pressure will be a little lower on the second floor compared with in the basement.)

As the boiler heats up to operating temperature the water will expand; that is what the expansion tank is for. With the tank pressure starting at 5 PSI the remaining air cushion in the tank will rise considerably in pressure as it is squeezed by the expanding water. Pressure rises similarly everywhere else in the system to your 30 to 35 PSI.

Whereas with the expansion tank preset at 12 PSI, very little water will enter that tank when the system is refilled for operation. When the sytem gets up to operating temperature the water will expand just the same but the larger air cushion in the expansion tank won't be squeezed as much percentage wise and its pressure (and the pressure in the rest of the system ) won't rise as much.

The expansion tank behaves in the same fashion as a pressure tank in a well water system but for the boiler the purpose is to give the heated water a place to expand into. The purpose of the air cushion is to prevent cooler water from filling the tank completely leaving no expansion room when the water is heated. The fact that the pressure of the air cushion changes inversely with the space remaining for the air cushion (and the rest of the system's pressure changes to match) is due to a (n inviolable) law of physics.
 

Last edited by AllanJ; 08-06-18 at 05:56 AM.
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Old 08-06-18, 05:22 PM
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Well the boiler ran awhile seeing I have a boiler mate hot water tank, the pressure went up to 20# and is holding there.
 
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Old 08-06-18, 06:21 PM
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That is good and I'd consider it acceptable.
 
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