Bleeding old cast iron baseboards

OldHouseNewOwner

I am trying to bleed old Base Ray cast iron baseboards. At the top end there is a 3/4” to 1/8” reducer fitting, then a plug with a square 5/16” head. The plug broke clean off when I tried to turn it. Am I better off trying to turn the reducer fitting itself? Is it easier when the baseboard is hot, or cold?

There looks to be a bleeder plug in the body of the radiator, but it’s been painted over…

The heating contractor that installed a new boiler last year seemed to have no trouble bleeding them, went to each radiator with a little cup of water. 

SuperTech

I have the same baseboards at my house and have never had to bleed them. Make sure you have a functional air removal device at the boiler and the expansion tank is charged correctly.  Raise the boiler pressure to 25 PSI and give it a good purge. Once you have all the air you can get out by purging, Raise three pressure again to 20-25 PSI and run the boiler for a few burner cycles allowing it to reach the high limit temperature.  Make sure the pressure stays brlow 30 PSI.You should hear air hissing from the air vent as the boiler runs. This is assuming that you have a bladder tank and air scoop. If you have a compression tank the process is different. If you get the air out return the boiler pressure to 12-15 PSI to match the expansion tank air pressure. 

It helps tremendously if your boiler is piped correctly with the circulator pumping away from the expansion tank and air eliminator.  Post some pictures of the boiler, that would help us assist you. 

OldHouseNewOwner

Hi SuperTech - Thanks so much for your response. Photos of the tankless gas boiler setup attached. That’s a good point, so I should purge the system instead of the individual radiator? I’m not sure how to increase boiler pressure. The PRV only has a button for “fast fill”, but it doesn’t seem to increase pressure. Should I isolate the zone I’m having an issue with (close supply and return valves of other zones), hold “fast fill” and open the faucet drain on the return side to try to flush air out? I could only find that one Hy-Vent above the boiler. Maybe that’s not enough venting?

EricPeterson

The radiators are missing a bleed fitting.
In your first photo, there is a tapped hole but the installed failed to provide the bleed fitting.
Here is what it should look like:


Eric Peterson

OldHouseNewOwner

Thanks Eric! Yeah I don’t have those bleed fittings on any of them. Don’t think the original installer from ‘57 is around anymore  That’s too bad, would probably make my system a lot quieter. If I tried to retrofit now, I think I’d end up drilling out the plug from each. 

OldHouseNewOwner

There is a manual vent on the HN-2 by Axiom, does that need to be opened? I let off some air until water came out, then closed it again.

https://axiomind.com/axiom_product/hn-2/

EricPeterson

OldHouseNewOwner said:

Thanks Eric! Yeah I don’t have those bleed fittings on any of them. Don’t think the original installer from ‘57 is around anymore  That’s too bad, would probably make my system a lot quieter. If I tried to retrofit now, I think I’d end up drilling out the plug from each. 

You might be surprised. With the right tools and some penetrating oil, you could probably remove that plug - when the heating system is over. I have these radiators on floors two and three and the only one I have to bleed is on the top level. Then install something like this.

Eric

Big Ed_4

If I remember those plugs were brass . Easy removal or drilling out.

To leave the air in the top of the baseboard leaves the system with two compression locations ... The circulator pulls from one to the other . The system gets sloppy ... It is important to have one compression location .

mattmia2

You have an auto vent on the hydraulic separator as well. It looks like your have the right valves to purge on the individual zones. Once you get it circulating any remaining air will eventually work its way to the hydraulic separator and be vented at that auto vent.

Edit: You would close off all but one zone and purge one zone at a time.

If it were just an air scoop it might not eventually get to the auto vent but the hydraulic separator will let the fluid slow down and let the small air bubbles settle out. This has to be the way the installer did it, they probably just went to each emitter to make sure it was heating.

Big Ed_4

Hopefully

OldHouseNewOwner

Hey Guys,

Thank you all for your advice, it’s what helped me solve the issue. I think the 3/4 pipe from the basement up to the main floor was air locked, it’s on that first radiator that I heard splashing sounds. 

I ended up isolating the zone and flushing it by running a hose from the return pipe to my utility sink. But I suspect I have low water pressure, because pushing “fast fill” on the PRV did nothing. I think my water pressure in the supply line is so low that’s it’s not even regulating anything. The regulator is screwed in all the way, at the max setting, and I get only 15 psi.

The system sounds are now back to what I’ve always thought of as “normal”. It sounds like the water line noise when you open a faucet. Is that normal? I thought it was caused by the circulators, but maybe it’s air trapped in the top of the radiators….


All the best,
Merlin

mattmia2

Usually the circulator motor is louder than any water flow sounds if the velocities are reasonable. Are the caps loose on the auto vents so they can vent?

OldHouseNewOwner

Thanks Matt. Yep, the caps on the auto vents above the boiler and the hydraulic separator are loose. Maybe it’s all good then.

OldHouseNewOwner

Checked the supply water pressure today (at a different location), and it was fine. To me, it seems like that PRV is broken. The “fast fill” button is just a loose plastic cap. No resistance at all when I push it, and pressure remains the same. Anybody have experience with that style PRV?

neilc

is that other location at the same elevation? same floor?
then the pressure is there,
are there supply valves or TRVs ?
is the weak one open ?