Bleeding boiler system for radiant heating?

Riven

I have an 8 zone radiant floor heating system (one zone is DHW in case that matters) with Honeywell zone valves, with a number of the ball valves being difficult to turn and not closing entirely (replacing the power heads helps, but the ball valves still don't close). I see how to isolate the valves and drop system pressure in order to replace the ball valves.

Doing this will introduce air.

My system has antifreeze (I don't know what kind) and should be protected to about -20F (based on plumber report using a refractometer). In a lot of YT videos, after introducing air into the system it looks like the air is bled out of those systems by running a lot of new water into the system until there are no more air bubbles - if I do that I'm going to lose the antifreeze. There are no radiators in my system, just radiant floor and DHW.

Above my expansion tank is an auto air vent - my question: is bleeding the air necessary if I replace the ball valves, or can the auto air vent handle the air that gets into the system? Or is the proper procedure to run a lot of water through to get the air out, then add antifreeze solution to restore freeze protection? Or something else?

Advice/guidance greatly appreciated and I'm happy to post pics if that would help.

Mike

leonz

Turn the thermostat all the way up for a couple of hours.

hot_rod

it depends on how much fluid you loose while making the change. Do you have a way to catch and pump the glycol back in?
An auto purger may get any air out, if you have one,

How old is the glycol? Do you absolutely beed glycol?

Riven

Thank you both for the comments so far.

https://forum.heatinghelp.com/discussion/comment/1829282#Comment_1829282

I have a submersible pump, so possibly (if there's enough to submerge the pump) I could return some of it to the system.

The antifreeze is about 20 years old. I've wondered how necessary it is - I live in the mountains at 7k feet, and it's gotten close to -20 once or twice in the last 9 years.

hot_rod

Get a ph meter or some ph strips. If the glycol is in the low 8 ph, I would not put it back in. 20 years is a long time for hydronic glycol

Low ph indicates the glycol inhibitors have been depleted and the fluid will become aggressive to the metals in the system.

Unless you have outdoor piping, glycol is an insurance policy. It can protect the system during a boiler or power outage. But if you live in the home full time, you will catch an event like that before the home freezes.

GroundUp

20 years is at the point it should probably be replaced anyway, at the very least refreshed. It's impossible to say whether or not purging would be necessary, but it's a very common need with low velocity glycol systems. If there is no garage in the zone and somebody is always occupying the space, glycol may not even be necessary at all.