Anyone?

It should be as cool as possible when bleeding the radiators but does not need to be stone cold.

I usually set the thermostat for at least ten degrees lower than the current temp in the room, and then let the system cool for an hour or two before bleeding radiators. However, since your baseboard system probably runs at a higher temp (maybe 180) than my 140 degree radiators, I might give it more like 4-5 hours to cool off.

My system has an auto refill connection to the house cold water line, so it will add water if needed. However, most times when I bleed the 8 radiators I only get a small amount of air before it starts sputtering and I have water running out. I don't think much water is added to the system unless you actually shut off and drain a radiator. I will also warn you that the water often smells bad when you bleed it out, but that is just because it is stale and without oxygen.

Bruce

Thanks. I have to rebuild two zone valves so it’s going to be a drain and refill job

I've only emptied my system once, when I switched over from all iron pipe to an iron pipe and PEX combination with PEX manifolds. I just turned off the water feed into the system, connected a garden hose to the drain pipe and pointed it into a floor drain. Then I opened up the drain valve, and a few radiator vents on my 2nd floor to allow air to enter the system at the highest point. IIRC, it took about an hour to drain the system.

Bruce