Purging the system–HELP

Have your “plumber” install a Hoffman #78 Water main vent valve. This is slightly over kill BUT it works. Now you should also have your contractor check all around the circulator to find out where ths air is being sucked into the system from. Unfortunately I cannot remember the swedish company that imports an air elimatior that removes micro bubbles.
Personally I think you had better find out where this air is getting in.

You should also have your plumber do the following.

1-Get a no flow hydrostatic head reading cold or warm water NOT hot
on the altitude gauge.
If he cant get this reading take a measurement from the top of your boiler to the upper most radiator and times this by the constant .434 this will give you a no flow reading.

2- Then figure your automatic feed is giving you 12-15 PSI set pressure so 12 times 2.31 = almost 28 feet in height BUT you need more pressure to give you a positive system so add 4 PSI by using the automatic fill device.
Now the total elevation should be 37 feet.
To see exactly what you need you can take the height .434 for example 28 ft high would give you 12.15 pounds WHICH is you convert back to 12 PSI 2.31 = almost 28 feet.
The reason this is critical is to keep a possitive pressure on this system BUT not high enough to blow the relief valve when the boiler fires up (temperature pressure relationship)the more heat the more the water will expand (up to a certain temperature) and that is why you should also have your plumber double check your expansion/diaphram tank. What could be happening also is your relief valve goes off allowing fresh water into your system and all fresh water has oxygen bubbles.

By boiling this water your releasing more bubbles in this system. Make sure your relief valve piping is visable and not choked down.

Check your gauge pressure before and after firing. sight unseen makes this hard to guess BUT these are some possibilities.

Good luck