Reduce Pressure

I have a two zone baseboard hot water heating system with a Utica boiler. Two circulator pumps with a purge valve below each. When my boiler is up to 180 degrees, the pressure gauge reads 21-22lbs. It's my understanding that it should be in the 12-15 lb range. My question is, "How can I reduce the pressure down to 12-15lbs?" In addition, as the boiler temp drops, the pressure drops slightly. Is that normal? Thanks.

 

A slight change from cold to hot is normal. You can reduce the pressure by opening any drain valve on the boiler or piping. If the pressure comes back up & holds there, the reducing valve has probably been adjusted. The higher pressure will hurt nothing nor should it be a concern unless it gets over 25#. If it were mine, I wouldn't mess with it. If it ain't broke don't fix it.

 

The pressure will rise and fall with the boiler temp. Depending on the size of your expansion tank, it may rise or fall ohhhh, say around 5 PSI or so. A bigger expan tank will see slightly less change. So, yes, it's normal, to a degree. If the cold pressure is like 12, expect 17 or so when it's hot.

Assuming you have a bladder type expansion tank:

If the pressure on the air side of your expan tank is too low, you will see a larger change when it gets hot. If it's WAY low, you may even pop your safety relief valve when it gets hot. This is because the expanding water has no "spring" to push against. If it's too high, you may see it drop to nothing (or even negative (vacuum)) when it's cold.

You can not measure the pressure on the air side of the tank when the boiler system is pressurized.

The system pressure is set by your PRESSURE REDUCING VALVE, which is in line with the water supply to the boiler. These are _usually_ set at 12-15 PSI from the factory.

You can drain a little water from the boiler to lower the pressure, but if your reducing valve is set too high, it will just make up the difference once you close that drain valve.

How many stories is your house ? That can make a difference in the system pressure.

If it changes more than say 5 PSI from cold to hot, you could possibly be looking at an expansion tank on it's way out...

 

Thanks for your help guys. If 20 - 21 lbs falls within an acceptable range, then I am inclined to not fix something that ain't broke. I was concerned about the pressure reducing valve "popping" if the pressure got over 25 lbs.

My house is 1 & 1/2 stories with a full basement. Boiler is in the basement. I have one zone in the basement which loops around 800 sq. ft. Second zone goes up to main floor of roughly 1200 sq. ft. and also goes up one more story and does a small loop of 200 sq. ft. in a "loft" with bedroom and bathroom.

Sounds like the pressure reducing valve and the bladder tank work hand in hand to keep everything in sync. Would that be a correct assumption? Thanks again for your help in this matter.

 

There's a pressure REDUCING valve, and a pressure RELIEF valve.

The reducing valve is a pressure REGULATOR which will allow fresh water to pass into the system if the system pressure falls below it's setting.

The pressure relief valve is usually a 30 PSI unit, and will open if the system pressure goes above 30 PSI.

The expansion tank is basically a spring for the water to push against when it is heated and expands. You can't compress just water, but you can compress air, so as the water expands, it pushes against the air cushion to help regulate the pressure in the system.

 

Just wanted to say "Thanks" for your help and for taking the time to explain how these things are integrated. I had called 3 - 4 P & H supply stores with similar questions and nobody seemed interested in helping me. This is a great site/resource. I'm certain I will have more question in the future. Until then, Happy Friday and Happy Holidays. PS - Gittin' dern cold up here in VT