I'm tempted to add a second lever valve in series with the first, in the ground floor utility cupboard next to the hot water tank.
Should the header tank overflow ever start pouring (or any other part of the system for that matter), it would make for a no-hassle shut- off, until the ballcock/whatever can be replaced/repaired (as well as making for easily controlled system filling).
However, there would always be the temptation for a future owner to shut it off and forget about it.
So trading off convenience against a potential hazard - your thoughts?
The system actually uses a 250L thermal store, so vast amounts of water would have to be lost before the tank/boiler (Rayburn 480K) circuit could get air into it.
I'm also planning to have lever valves on the two tank-to-radiators circuits to isolate them independently from the tank - but obviously *not* on the boiler/tank circuit (apart from the valves either side of the pumps).
Lowest point(s) in the system will be the 3 pumps (2 heating circuits, 1 boiler circuit - so it's "pump plan"), so this seems the obvious place to add drain-off points. ISTR it's smart to raise the dop's slightly wrt to the lowest point to prevent them sluding up. Same with the pumps - have a *slightly* lower point for the sludge to collect?
I *think* there should be no need for air bleed valves, apart from those in the rads - in normal use. But some extras might be useful for system filling, and I can see that the dop's next to the pumps might make for the easiest initial/partial system filling.
Comments/suggestions from those with similar systems or experience?