Old Boiler - Air In System - Solutions?

BoBoBot

Hi everyone! New guy who joined the forum for some pointers on my old boiler system. Over the past few years, I have been having intermittent issues with air in the system. Had an issue last year with low pressure and a local plumber changed out the old auto feeder. Pressure has been great.

Issue right now continues to be the air trapped in the system. House is a split level with 3 floors and a finished attic. Heating system has 3 zones, the third one feeding the 3rd level and then the upper finished attic. Zone 2 does the living, dining, and kitchen, Zone 1 does the downstairs den and office. There is no basement.

House is warm, heats up, and baseboards are warm. You can just hear the water in the pipes and you shouldn't. There is a small Maid-O-Mist on the system. Cap is loose to allow air to escape. There are no additional bleeders on any of the baseboards in the house with the except a hose bib bleeder on the baseboard in the finished attic (the highest point). I've had issues in the past with that baseboard getting cold and having to bleed the excess air from there. That has not been the case so far this winter, the system is just noisy and you can hear air in the system.

I've attached pics of my system with the exception of the hose bib valve on the upper baseboard.

My questions:
-In one pic you will see an area that I circled with a question mark. My thought is to install a Spirovent there, however, I noticed that most setups with it have the expansion tank in the same area. Can I install a Spirovent here and be done with my air issues?

-Other question is that old expansion tank. Would I see better performance if I changed it out?






I know it's an old bladderless one.

Thanks for any help!

Jamie Hall

The old compression tank is probably fine -- considered on its own. It may be waterlogged, however -- which you would see by a marked variation in pressure from the system cold to the system warm. That may be easy to correct -- with patience, as I note a black hose connected to its drain valve which, hopefully, goes somewhere harmless. The drill is to close the ball valve on the line to the tank and drain the tank empty, then close the drain and reopen the ball valve. This will re-establish the air cushion.

However.

The way that tank is piped to the system is not correct. It should be connected to the system main via a pipe going straight up off the main to the tank, so that any air passing by in the main goes up to the tank. It isn't. Worse, there is an air vent on that line -- if I read the pictures correctly -- so that at least some of the air which should go to the tank escapes. The end result of this is that the tank will lose its air charge, sooner or later -- probably sooner.

So -- nothing wrong with the tank, just with the way it installed.

On the whole, it may be simpler (and certainly easier for a modern technician, who may never have even heard of a compression tank) to take it out of service completely, and install a modern expansion tank -- which won't last as long, but is easier to understand. However, where it is hooked into the system is important. It should be installed close to, but not right at, the inlet side of the main system pump (which I can't really make out in the pictures). The Spriovent -- or other air removal device -- should be installed ideally where the system pressure is greatest -- which will be on the pipe downstream of the main circulation point -- and where the water temperature is greatest. Which may not be the same place.

If you can furnish a diagram of the system, someone will give you a better idea as to where things should be placed.

ch4man

dont do it. with an old school x-tank like you have, there should be NO auto air vents. the one you have should be removed.
n the first picture, on the return is a gate valve and drain valve just next to it. that is where the air purge for the entire system is done.

both style of x-tanks are fine. the one you have has nothing to wear out or break. I like'm

ch4man

what really bothers me is that it looks like that auto bleed replaced the very important safety valve. or maybe it just never showed in your pictures..
show us a few more pictures. to me it appears the compression tank is in the supply piping right on the top where there is nothing to keep any air from landing in the tank where it belongs

EBEBRATT-Ed

I would install a new bladder tank and a spirovent or =. For best performance you should "pump away" from the expansion tank.

It looks like your circulator is on the return to the boiler, they should be on the supply.


But before you go to that expence, drain the expansion tank and remove and plug the automatic air vent and any other automatic vents if you have them. Use a manual valve or bleeder to bleed the system
As @ch4man mentioned you can not use auto air vents with a plain steel compression tank. They will let air into the system. This could be part of your issue.

Try this first

BoBoBot

Thanks for the replies so far. The pressure remains consistent whether the boiler is on or off. I have only changed three things on the system since I bought the house. I had a plumber put on the auto feeder, I put the shut off valve to the expansion tank to make it easier to drain and I replaced the Maid-O-Mist air vent. The air vent that was originally on there was corroded and capped shut. I figured it should be opened and when I tried to, the old one just spewed water. So I put a new one on figuring it belonged there.

So based on the replies right now, I tightened that cap down on the air vent. Usually after the system shuts off, I will hear air bubbling into the expansion tank for a minute or two.

I'll grab some more pictures tomorrow and try to draw up a diagram. So that expansion tank should be drained completely? Like, don't even leave a little water in there?

Jamie Hall

Correct. Close the valve to the system and drain the compression tank completely. Not even a little bit of water. Then close the drain and open the valve to the system. You will probably have to add some water to bring the system pressure up to whatever -- say 15 psi. That will establish the correct air cushion in the compression tank.

Then if you take that air vent off (go looking for others -- automatic vent on a radiator somewhere?) any air in the system will -- eventually -- make it to the compression tank, where it belongs. This may take a while with the piping as it is.