Boiler pressure - Does this need adjusting?

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Old 11-08-15, 02:21 PM
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Boiler pressure - Does this need adjusting?

My oil fired boiler pressure is at 22 PSI; it seems high. After reading a few threads, I bought a 0 30 PSI pressure gauge to verify the pressure. When the system is cold (not running for say 24 hours other than keeping the boiler temperature at 160 - 180 degrees), the pressure is 20 PSI. When the thermostat calls for heat, the circulator pump goes on, and the PSI immediately drops to 16.5. It then climbs to ~18.75 PSI before the burner goes off. It will then drop to ~16.5 PSI before the burner goes on again, and then repeat this cycle.

When the thermostat stops calling for heat and the circulator pump goes off, the pressure immediately jumps to 22 PSI, before dropping over 1.5 or so hours back to 20 PSI.

In a search of the forum, I found this comments from NJT:

No. 30 PSI is too high. COLD boiler should be 12-15 PSI. HOT boiler perhaps 8-10 PSI higher.
Is my boiler pressure too high to start with? Should it be lowered to 12-15 PSI?

If so, is lowering the pressure as simple as just draining off a little water to drop the pressure? I'm assuming the PRV will backfill that water, just that the boiler will now be at a slightly lower pressure to begin with. Is this correct?

Thank you.
 
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Old 11-08-15, 02:53 PM
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22 psi is not too high a pressure. Most residential hot water boilers have a maximum allowable working pressure (MAWP) of 30 psi and the safety valve is set at this pressure. Some boilers may have a MAWP as high as 60 psi.

The maximum pressure you should run is about 90% of the safety valve set point, or in the case of a 30 psi system...27 psi.

The pressure that the system will run at is dependent upon the setting of the make-up water pressure reducing valve (PRV), the air cushion in the expansion tank and the usable volume of the expansion tank vs. the total volume of the system.
 
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Old 11-08-15, 04:37 PM
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pressure

Sounds like your gauge is located near the suction side of the circulator. That's why the pressure drops when the pump starts, and jumps back up when the circulator pump stops. Sounds fairly normal to me-
Steve
 
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Old 11-08-15, 06:42 PM
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Pressure and fluctuation is all okay - good!

Sounds like your gauge is located near the suction side of the circulator.
Actually it is on the return side of the system.

Thank you to both.
 
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