On Sun, 02 Jan 2005 13:22:40 GMT, Bubba
wrote:

On Sun, 02 Jan 2005 12:50:27 GMT, (Gary R. Lloyd)
wrote:

On Sun, 02 Jan 2005 12:19:27 GMT, "Tom Ingle"
wrote:

You probably don't have enough pressure in your boiler. Check your pressure
gauge to see how much you have. Every pound of pressure is equal to 2.31
feet. So if your highest radiators are 30 feet above the boiler then you
would need at least 13 pounds of pressure at the boiler just to raise the
water that high.

While I agree with the above, I would add a couple points:

1. It is always a good idea to have a little extra pressure, so I
recommend measuring the height of the system and dividing by 2. For a
30 foot system, I recommend setting the minimum pressure at 15 psi.

2. When the boiler is heating, the water expands, increasing the
pressure. This extra pressure from expansion must be removed before
measuring and adjusting the pressure. This can be accomplished by
turning off the boiler and pump, then draining off water from the
boiler until cold fill water starts feeding into the system. Close the
boiler drain and wait. When the water stops feeding into the system,
this is your minimum pressure.


Why does the pressure increase and water expand if you have a properly
opreating expansion tank?

Water always expands when heated. That's just basic physics.

Without the expansion tank, the pressure would rise very rapidly
because water cannot be compressed. With the expansion tank, the
expanded water pushes up into the tank, compressing the air.

The pressure of both the water and the air are increased as a result
of that compression. How much the pressure increases depends upon the
amount of expansion and the size of the tank. There is always some
increase in pressure.

Adjust if needed, then turn everything back on and bleed the system
starting at the top.

Bleed the system starting at the top????????
Nope. Never

Why not?

If you do it right, you will probably never have to bleed the system
again.

In theory, maybe, but not in the real world.
Maybe we are on 2 different "pages" here?
Fill me in.....
Bubba

Generally there is some sort of automatic vent for the very tiny
amount of air entering the system with the fill water. Usually, if a
system needs repeat bleeding it is because there is insufficient fill
pressure, resulting in a vacuum at the top of the system whenever the
boiler is cold.

Note: When the water is pumped into the boiler rather than away from
the boiler, there may (or may not) be a vacuum at the suction side of
the pump, in which case additional fill pressure may be needed.

_______________

Gary R. Lloyd CMS
HVACR Troubleshooting Books/Software
Written by a veteran Service Technician

https://www.merchantamerica.com/tmethod/