How to drain baseboard heating system on very old boiler (pics)

dadintraining

My wife and I just purchased a home and I’m doing my best to learn about all of it. We have a very old gas boiler that goes to 2 zones. I believe there’s a good amount of air in the baseboards because when it runs the whole house sounds like a water park. The air scoop looks like it was installed incorrectly (less than 18” of pipe before it), and even if it wasn’t it’s very corroded and likely no longer working. I’m doing some renovations and would like to drain the system to remove a section of the baseboard and replace some corroded parts, the back flow preventer, pressure regulator, air scoop, and expansion tank prob all need to go. Some problems I’ve come across. There are no air bleeder valves on the baseboards, isolating the zones seems tricky because of how the system was set up, and there are a lot of old corroded parts. I have some ideas but would like to hear what others have to say. I’m also considering replacing the whole thing because of its age, but the boiler itself seems to be working just fine, even with all the air in the lines it heats up the whole house no problem, so it seems like a waste to replace it. 

Jamie Hall

That actually doesn't look that terrible, on the whole... there are some things which may need replacing, but overall it looks pretty good.

Draining it shouldn't be hard. Someone gave you useful valves. Some things, like the expansion tank, may not need replacing; check how the system pressure behaves when the system heats up (once you get the air out...). That air release does look a bit sketchy. In general, though, make sure that something is actually not working before you start throwing parts at it.

dadintraining

The back flow preventer has a slow leak which is prob causing all that corrosion, so I figured I’ll replace the pressure regulator along with it. The extension tank does seem to be working properly, but I can’t imagine that air bleeder above it is doing anything, and I think if I try to replace that the connection on the tank will break, it looks very corroded. I drew a sketch of the whole system, could use some ideas on how to drain it. 

hot_rod

If you are going to work on the fill system, move the expansion tank down there. Then you will be pumping away, and air problems will go away.

The air vent needs to be replaced also.

EBEBRATT-Ed

Things don't look that bad to me. I would replace the air vent on the air scoop. The air scoop is fine its just rusty from the vent leaking. You have purge and balance valves for each zone thats how you get rid of the air. Below the zone valve on the smaller zone you have a ball valve and a boiler drain. To bleed you close the ball valve put a hose on the drain valve and open it and feed water into the system. Purge till the bubbles stop , then do the other zone.

Move the expansion tank (or put a new one in) and tee it into the boiler feed water line between the feed valve and the boiler. The water feed line and the expansion tank have to be connected to each other and to the boiler on the same side of the circulator. In you case leave the circ as is and move the expansion tank You have a purge and balance valve above the boiler for the other zone

dadintraining

EBEBRATT-Ed said:

Things don't look that bad to me. I would replace the air vent on the air scoop. The air scoop is fine its just rusty from the vent leaking. You have purge and balance valves for each zone thats how you get rid of the air. Below the zone valve on the smaller zone you have a ball valve and a boiler drain. To bleed you close the ball valve put a hose on the drain valve and open it and feed water into the system. Purge till the bubbles stop , then do the other zone.

Move the expansion tank (or put a new one in) and tee it into the boiler feed water line between the feed valve and the boiler. The water feed line and the expansion tank have to be connected to each other and to the boiler on the same side of the circulator. In you case leave the circ as is and move the expansion tank You have a purge and balance valve above the boiler for the other zone

Glad you guys don't think it looks too bad! I get the idea for purging the smaller zone, but how would I purge the larger zone which doesn't have a drain or shut off valve after the zone valve? If drain it at the lower valve I cant feed it water to purge. As far as moving the expansions tank, would I move the air scoop with it, or leave that where it is? Can I hang the expansion tank just passed the pressure regulator and leave the rest as is?

psb75

Change out ALL of the badly corroded air-release cannisters. Air scoop is ok. Butt you you can change it out for a new Spirovent micro-bubble remover.

EBEBRATT-Ed

15th picture from the top shows a drain and a purge/balence valve for the larger zone. Yes leave air scoop. Move expansion tank to make up water line between boiler and pressure reducing valve. You may have to repipe a little to get it in there. Also looks like there is an old air vent on the large zone above circ pump change that out if it doesn't work. To bleed you add water it goes down through pump through boiler out the supply pipe through the baseboard and back the return line and out the drain with the purge valve shut to keep water from coming back up the return from the boiler. Open zone valves manually with lever while bleeding

hot_rod

As it is piped and pumped now the high air vent  could actually be allowing air into the system, under some conditions, low static pressure for example

Change the expansion tank location, maybe even cap that vent off.  The air purger and vents at the heat emitters should be adequate.

dadintraining

EBEBRATT-Ed said:

15th picture from the top shows a drain and a purge/balence valve for the larger zone. Yes leave air scoop. Move expansion tank to make up water line between boiler and pressure reducing valve. You may have to repipe a little to get it in there. Also looks like there is an old air vent on the large zone above circ pump change that out if it doesn't work. To bleed you add water it goes down through pump through boiler out the supply pipe through the baseboard and back the return line and out the drain with the purge valve shut to keep water from coming back up the return from the boiler. Open zone valves manually with lever while bleeding

I was wondering about that drain and valve. There are 2 of them for each section of the larger zone, just before they combine before returning to the boiler. They are about 20+ feet from the boiler so that section wouldn't be purged, but hopefully that not a big deal. Is there any concern with purging through the boiler? Wouldn't the pressure activate the release valve? As far as replacing the old air vents and moving the expansion tank. I don't think there's a way to valve off just the tank right now, so will I need to drain the whole system to do that part?