Another heating radiator question

Inside the house, the previous owner connected the plumbing to the old closed system, but bypassed the old, broken oil burning boiler. The radiators are old cast-iron, with the water flowing in and out of ports at the base of the 2' high units.

We can not seem to keep air out of the radiators! I close a valve at the end of the last radiator, turn up the thermostat to start the circulator, and bleed each radiator until they are full of water. Within a day or two, we hear water gurgling in the system.

I can't find any leaks. The radiators are higher in elevation than the outdoor boiler tank, so I suspected that the water was running 'downhill' when the circulator pump shut off. I added a zone valve at the end of the loop, which shuts whenever the pump stops, but it doesn't seem to make a difference.

Can anyone educate me as to what has been set up wrong?

You have two different types of HW heating systems connected together. I would bet that there is a major plumbing problem between the two systems and is beyond the scope of any internet forum as it will be nightmare for even the most advanced tech to diagnose and will cause an engineer to shake his head more than once.

T_Bone

As soon as you pressurize it, there's a whole host of people wanting to inspect it & test it for big $$$.....

--->Paul

Folks,

Thanks for your advice. It does seem that the radiators should empty out of the top. This is a simple system, but I've attached a drawing to help.

--->Paul

The other bad feature of a system such as this is the air bubbles (oxygen) carried through the system greatly worsens rust damage to the pipe fittings and boiler.

A typical hydronic system has an air separator to vent all air that accumulates in a raised chamber in the air separator, and the system is kept at a constant 12 PSI by a bladder tank that keeps the water and the air cushion separated.

Is your boiler a factory product that is capable of being used in a 12 PSI system?

If it is an approved unit, there will be an ASME rating plate on it listing approved pressure, which on an approved unit will be well over 12 PSI.

To sum this up... If your boiler is capable of use at 12 PSI, and you set up a closed sytem with an air separator and air cushion tank, after a day or two of the air separator venting air, the system will settle down, and the piping and radiators will be quiet of bubbling and gurgling sounds. You might have to bleed the radiators at the start of each heating season, but that should be about it.