Bleeding rads on open vented system

[Bogart]

On a thread I started recently , cannot find which one, somebody mentioned that bleeding of the rads on an open vented system should be done with the pump off so as to not possibly draw air into the system. Do I read into this then that auto bleed valves are not a good idea on that type of system for the
very same reason?

 

[ShaunCorbs]

auto air vents auto seal so you would be fine either way unless the auto air vent is broken eg venting water

 

[Bogart]

Thanks I was not sure. My system, inherited, seems to have a mixture of manual and auto valves, one of which a Honeywell type is kaput so will get a replacement.

 

[Last Plumber]

On a thread I started recently , cannot find which one, somebody mentioned that bleeding of the rads on an open vented system should be done with the pump off so as to not possibly draw air into the system. Do I read into this then that auto bleed valves are not a good idea on that type of system for the
very same reason?

I would go for manual vents. AAV's are notoriously leaky. Bane of my life, well one of the bane's anyway.

 

[Bogart]

On the Honeywell site it states that the vent should be fitted on the positive side. Is this due to the possibility of drawing air in on the negative side or not? There is one either side of my boiler!

 

[Last Plumber]

On the Honeywell site it states that the vent should be fitted on the positive side. Is this due to the possibility of drawing air in on the negative side or not? There is one either side of my boiler!

Yes.
Do you know where the neutral point of your system is?
From that point to the back of the Pump is more often than not negative and the front of the pump back to the negative point is more often than not, positive.
If you follow that.

 

[Bogart]

Am I correct in thinking the neutral point is where the 15mm pipe from the F&E tanks meets the pipework of the heating. Mine meets just at the pump on the inlet side, which I assume you mean by the back of the pump.

 

[Bogart]

Mine is like this.

So looking at that most of my system is positive pressure, hence the 2 auto valves either side of the boiler. Never knew about the 150mm max between F&E pipe and the discharge pipe. Both of mine actually eminate from an air separator.