How long should a boiler take to fill and purge air?

Jim R.

I replaced a leaky air-eliminator on my baseboard heat. 5 minute job, or so I thought.

First I drained 2-3 gallons from the boiler so I don't flood the floor removing the vent. Vent replacement went just fine. Turned on the cold water boiler supply to refill and heard water going in, through the pressure reducer (Watts 1156F). So far so good.

But when the heat went on I could hear water circulating through the pipes. The Supervent air eliminator at the boiler bubbled for the next hour and it did get quiter but 4 cycles later you can still hear a faint waterfall sound coming down the pipes. How long before things are back to normal or does it sound like something is wrong?

Normally I keep the cold water boiler supply closed so it's not constantly trying to intake water into the system. I check the pressure every so often in case there's a leak but never had one. This is the first time I took this amount of water out in 5+ years. I remember the boiler guy saying that old water was better than fresh water, as long as the pressure is right.

Pressure was 12psi after the top off, which went up to about 15psi at 190degrees, now back to 12psi cold. I'm not sure what the pressure was down to after I drained the water.

Ironman

It really depends on how it's piped, zoned and pumped. As long as you're holding good static pressure and you've got circulation, I wouldn't worry about it. Give it a couple of days.
How many stories is your house above the boiler?

Jim R.

Just a single story, boiler in basement. Two zones, one for baseboard heat and one priority for DHW.

i'll give it some time. I was expecting it to purge out fairly quick once it got to temperature but I guess not. Pressure is fine and so is the heat/HW so I guess it's OK.

Thanks.

Ironman

Just remember: the air separator can only remove air that passes through it. And, it won't get all of it on one pass. If the piping and pump are arranged and sized properly to keep the velocity at 2-4 feet per second, then entrained air will be returned through the air separator. Keeping the static fill pressure a little higher will aid in the process. Just be careful not to set it so high that the relief valve opens when the boiler is hot.

Also: I would NOT close the fill line unless you have a low water cut off on the boiler. If you spring a leak somewhere, you could be creating a bomb that could level your house. Leave the shut off valve cracked open enough to keep pressure on the boiler.

unclejohn

Here we go again. Open vs closed.

Ironman

unclejohn said:

Here we go again. Open vs closed.

If you go back and check that infamous thread, you'll see that elected not to comment on it.

Jim R.

Thanks guys. I wasn't aware it would take overnight for the air to come out. Sounds just fine now, main vent isn't bubbling anymore.