New expansion tank = no more air in baseboard heating zone?! Pic in post.

Rob94hawk

My expansion tank went bad and filled up. Then only one of my heating zone pumps started squealing and I couldn't keep air out of the 1st floor baseboard heating. So I thought this meant there was a spike in water pressure and put a hole somewhere in the pipes which are in a slab! I had to keep bleeding air from the slab baseboard heating but not my upstairs zone. The water pressure on the boiler stayed at 5 psi this whole time so I figured there had to be a leak.

The service guy came yesterday and replaced the expansion tank, bled the lines, and now everything "seems" to be back to normal. The pressure is now a steady 20 psi while not running. But it's only been ~48 hrs. The pump in the pic is to the slab baseboard heating right next to the expansion tank. If it was the expansion tank that caused the air in only one zone I'd like to understand how.

Should I call a plumber to check for leaks in the slab? The house was built in 1972. Thanks.

Jamie Hall

You'll know if there's a leak in the slab: the pressure in your system won't hold. shut off any autofeed device and Just watch the pressure gauge.. No need for a plumber at the moment at least.

Rob94hawk

Jamie Hall said:

You'll know if there's a leak in the slab: the pressure in your system won't hold. shut off any autofeed device and Just watch the pressure gauge.. No need for a plumber at the moment at least.

I thought the baseboard heating was a closed loop?

Edit: I'm not sure if the first pic is the main feed. I turned it off and no pressure drop. It looks like there is more than one feed.

EBEBRATT-Ed

The valve with the white handle near the tag that says "A100 60A " which is the burner nozzle size


When an expansion tank goes bad a lot of weird things can happen. The expansion provides a cushion to keep the water in the closed loop system under constant (more or less) pressure as the water heats and cools.

If the tank goes bad and you have no cushon you will get over pressure when the water heats and very low pressure when it cools.

Normal pressure is about 15 psi cold to 25ish when hot. It should pretty much always stay within those pressures in most cases.

Rob94hawk

Just can't wrap my head around air getting into the lower system but not the upper baseboard heating.

Regardless, had a plumber come just for peace of mind. He opened up the main water meter on my property and he explained that if you had a leak, the triangle on the meter would be moving. We watched it for a while and no triangle spin.

Learned something today and got peace of mind along with it. For now. It's a 50 year old house.

EdTheHeaterMan

Rob94hawk said:

I thought the baseboard heating was a closed loop?

Yes, you have a closed loop system. That means there is no water leaking in or out, if it is working properly... SO... If there is a leak, then water will leave the closed loop SYSTEM by way if the leak and the water feeder PRV will add water to replace what is leaving. With no movement on the meter, and the boiler pressure staying stable, then you have on leak.

The floor loops and the baseboards are all part of the "closed" system. Just like each baseboard radiator zone is it's own loop but they are all connected to the boiler in some way. And that way they are all connected is part of the "close" SYSYEM

Rob94hawk

Since the expansion tank replacement there is no more air in lower baseboard heat pipes.