Too Much Pressure

I have a residential boiler that keeps running over 30 PSI causing the pressure relief valve to drain on the floor.
When I first examined the system, I noticed the expansion tank (with diaphram) was completely filled with water. I replaced the expansion tank with a new one and turned the system on. The pressure still exceeded 30 PSI.
How do I find the source of the excessive pressure and fix it?
There is a reducing valve that says 12 PSI on the factory label. Going
into the reducing valve is a cold water supply line with a shut off valve. It looks as if a previous repairman has backed off the adjusting
screw a few turns from the factor setting since there is the absence of
red paint on some of the threads.
I have not adjusted the reducing valve nor cleaned the strainer.
I can drain the system, get the pressure down, fill the system to about
12 PSI and then run the system:
- If I run the system at this point with the cold water supply valve closed the system appears to stay around 18 PSI. My gut tells me I need to keep this supply valve open when operating the system to safely
supply new water to the system if needed.
- If I run the system at this point with the supply valve open, the pressure will go up to over 30 PSI. If I then let the system cool, it appears that the pressure will go down to only about 18 PSI. Why doesn't the cooled down system go back to the 12 PSI condition as when I started it?
Should the water supply line going into the reducing valve be kept open
when normally operating the system?
Should I try to adjust the reducing valve?
Should I try to clean the strainer on the reducing valve?
Should I adjust the 12 PSI pressure on the new expansion tank?
The water temperature appears to reach about 155 degrees after an extended period. Should I reduce the water temperature to reduce the pressure? What's an idea residential boilder water temperature?
FYI - the house is 3 stories above ground so I need to circulate water 35 feet from the basement. Some threads lead me to calculate that I need about 20 PSI to circulate water that high. If that's accurate, how do I keep the pressure between 20 and 30 PSI.
Sorry for all the details and asking too many questions here but thought they might help give one of you experts a hint as to what the problem may be.
Any advice on solving this boiler pressure situation would be appreciated.
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it sounds like you need to replace the pressure regulator valve with one that operates in the 20-30 pound range - rather than the current 12 pounds in order to insure water to 3 stories.
did you pressurize the expansion tank after you replaced it?
If not, you should to maximize expansion capacity.
Have you or can you validate that your gauge is correct? If not, you should.
Since you want to have about 25 pounds of pressure, your gauge should have about of a 50-60 pound max, so that the working range of the gauge is in the middle.
the water that enters the system is probably cooler than the temp after cool down. Therefore, the pressure won't drop all the way down to the level that it reached with the cold water used in the initial fill.
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at 15 greenfield, buffalo ny altitude we need 25 pounds WHEN HOT AND CIRCULATING to get from the basement to the third floor hot water boiler radiators. our temperature is set to max at 180 but it depends on your system. our expansion tank has no bladder and we set it to half water half air when cold. you must refer to installation manuals on all parts of your system.
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Under pressure, one psi will raise water 2.3 ft. It doesn't matter if it's Buffalo NY or Death Valley CA. The average 3rd story radiator is less than 30 ft. above the boiler, and needs no more than 13 psi. If you need 25 psi to heat the 3rd floor radiators, they must be about 57.5 ft. above the boiler.

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Do you have auto water feed, it is probably bad, close it , drain to 12 when cold and see what happens. if it raises 3 lb hot leave it is normal. If you dont get 3rd floor heat raise it manualy a lb at a time-when cold till 3rd floor radiators get heat, you will have to bleed radiators if there is no heat also . You only need as much pressure in the system to get 3rd floor heat. Less pressure means longer boiler life.
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bob villa says: http://www.bobvila.com/ArticleLibrary/Task/Building/WaterHeat.html "With traditional baseboard heat, water leaves the boiler at approximately 180F to 200F and is sent through pipes throughout the house via a pump or circulator. The hot water enters various heating loops and conducts heat to the pipe, or panel to which it is connected. Once the heat has been transmitted to the surface or fins, the air within the room is warmed principally by convection. In this system, cold air is drawn across the warm surface, absorbs warmth as it passes and then moves upward. Cool air from below the heating unit is constantly being drawn into the unit as the warm air rises and flows on to spread warmth throughout the room.
Baseboard Heat The most common type of hot water heat in the United States is finned-tube baseboard heat. Located close to the floor, finned-tube emitters are usually housed in metal enclosures that have reflective material behind them to encourage heat transfer from the fins or slats to the air passing over them, rather than being lost via conductivity through the cold wall behind it. The hot water pipes emerge from the floor and run directly behind the enclosure with thin, metal slats or fins, placed close together all along the pipe. Heat is transferred from the water to the pipe and ultimately to each of these fins. The fins serve as multiple heat emitters, warming the cold air from below. Enclosures must be located at least one to two inches above the finished floor to allow for adequate air circulation and heat transfer.
Piping There are actually a number of different layouts for hydronic heat, but they all serve the same principle: Hot water leaves the boiler in a supply pipe, transmits its heat along the way, and returns to the boiler as cooler water (typically 150F to 170F) , ready for reheating and redistribution. The basic variable in the equation is how long the hot water stays out there before returning to the heat source. Obviously, if there are a number of registers or panels along the way, the water will steadily lose heat, delivering most of its heat in the first registers and imparting less warmth to those registers at the end of the loop.
To account for this strain on the system, different piping layouts are used and zones are incorporated to provide more even heat throughout the home. The simplest of all piping layouts is the series or single loop system. Here, water simply flows through the pipes, into each of the radiators along the way, without diversion. Since the water will have cooled about 20F by the time it reaches the last radiator, this last emitter is typically sized much larger to take full advantage of the heat remaining in the water. A one-pipe system is slightly more elaborate and provides tees to divert water into each emitter along the way. In this way, radiators can be individually controlled so that heat need not necessarily always go to the first room on the loop."
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If you have a new diaphragm type expansion tank, they normally come pre-charged. It sounds like the automatic water feeder is passing water. Shut the valve off and if the problem stops, replace the automatic water feeder.

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