Air getting into hot water baseboard

jackburton

Hi! I'll start by saying that I know next to nothing about this stuff, unfortunately. My wife and I bought a house last year that had a roughly 60 year old boiler. This fall, we replaced it with a 120 BTU slant fin. Soon after we started using it, we were able to hear water rushing through the pipes, so air how somehow gotten into the system. I'd assumed it was from the installation. I had the installer come back to help purge the system (I had tried, but didn't really know what I was doing so I stopped and asked them to come do it, which they did). That solved the problem for a week, but then the sound came back. You could hear the water flowing through like a river, and could also hear a sort of washing machine sound from the boiler (I'm guessing it's the pump?). I took notes when they purged the system, so this time I did it myself. It's been about a week again, and it seems to be coming back.

I reached out to the installer to see what his thoughts were, and he seems to think it could be a leak in the pipes that are going through my slab. He wants me to use a leak detection service to see. I wanted to get some opinions on whether this could be anything else, because I'd like to avoid digging through the slab if possible haha.

Some additional details -

- when we purged the system, the water was very dark both times
- when I first tried to purge the system (before I took notes from the installer), I used too much pressure from the city water and water came out of the relief valve a couple times (not too much, but it happened). I think I'd also not had either of the zones open correctly, so the overflow happened very quickly. Could this have ruptured the expansion tank, and could that have anything to do with it?
- When the boiler was first working in the fall, before we noticed the water sound, it would sometimes make a very loud sound at some points (when it was shutting down I think)
- there was a point when the boiler would get really hot (in the 220s or so) for brief periods of time. I don't think this is happening anymore though
- we did remove a register in a room and rerouted some of that pipe through slab in my kitchen. my guess is if there is a leak it's there, but I don't know for sure. This was done before we moved in though, so it's weird to me that it wouldn't have happened last winter with the old boiler.

I think that's mostly everything. Thanks to anyone who takes a look!

Jamie Hall

Well now. The air can only get in if the pressure in the pipe is less than the air pressure outside the pipe. Therefore... the first question is, what is the water pressure in your system? Somewhere on or near the boiler there should be a pressure gauge (probably has a temperature gauge, too). Would you read that and tell us what you find?

Also, is there an expansion tank -- and how big is it, if you can find out. And is there an autofill valve (might be called a pressure reducing valve)?

jackburton

The pressure looks like it's about 12 PSI right now. Not sure if that fluctuates/etc. There is an expansion tank, not sure of the size. maybe about 5 gallons? Here are some pics

Rich_49

Would it be possible to get another couple pics of the boiler from a bit further out so we can see the near boiler piping and where things are situated in the system ? This would be a big help

EBEBRATT-Ed

Need more pictures stand 8' away all around the boiler and piping

jackburton

Sure, but I might have to take it later. Coincidentally, I'm getting new carpet in my basement and we put a lot of our crap right next to the boiler, so it's hard to get pics. let me see what I can do

jackburton

This is about as good as I can get right now. Thanks!

jackburton

A couple more pics

jackburton

mattmia2

Was there an expansion tank hanging from the ceiling for the old boiler or what did it have? Was it removed?

The test for a leak would be to turn off the water feed to the PRV(pressure reducing valve) and see if the pressure goes down. Watch it to make sure you don't operate the boiler without enough pressure, I would check once an hour to begin with, then lengthen the time if you don't see it falling up to checking daily for a week or 2.

The pressure will go up some when the system is hot and down when it cools, but if the PRV has filled it to 12 psi cold it shouldn't go below that unless you have a leak or have removed some air.

Air can get sucked in through a leak if it goes in to negative pressure, but fresh water also has air dissolved in it that comes out when you lower the pressure and raise the temperature.

What happened to the old boiler? If you had a leak that was unnoticed and a PRV that was keeping the system full, that new water with new oxygen could have taken out the old boiler.

HomerJSmith

Make sure the cap on that thingy on top of the expansion tank (Supervent) is loose and not tightened. It allows air out of the sys. That's the projection sticking out of the top of the supervent.

Do you have bleed air vents on the on the baseboards (my assumption)? Sometimes a too large a pump will create those types of problems.

I have used street pressure to flush and fill sys, no problema. No the EX tank isn't harmed.

The dark water coming out of the sys at change over could be anti-freeze that's gone bad because of age.

Street water can have several gallons of air entrained in the water that the supervent is designed to capture and eliminate. That Supervent should have been cleaned and checked at the change over, if it's not new, especially with black fluid in the sys.

When air is entrapped by the Supervent, a float drops and opens a vent that allows the entrapped air to escape. The float must move freely for it to operate properly.

jackburton

There was an expansion tank hanging from the ceiling for the old boiler. It was a bit bigger and more cylindrical in shape. Unfortunately, I don't have a pic. It was removed when they installed the new boiler, replaced by the one you see in the pics.

So if I turn off the water to the PRV, I can run the boiler as long as the pressure doesn't drop, correct?

The old boiler wasn't malfunctioning or leaking (that was noticeable, anyway). We just happened to come into some money and decided to pull the trigger on something that we knew would have to be done at some point, as the boiler was from the 60s.

jackburton

We have these nuts on the elbows for the baseboards. Not sure if these count as bleed vents. As you can see, there is some corrosion there. No leaking though as far as I see

Jamie Hall

Those nuts should count as bleeds. Provided they work...

mattmia2

They are manual bleeders, they shouldn't be capable of sucking air in.

Yes, you can run the boiler with the water supply shut off as long as it keeps pressure. In fact there is a debate about if it should be left on or off in case there is a catastrophic failure somewhere so it only dumps out what is in the system, not a flood of essentially an open water line.