Rob Graham wrote on 23/08/2020 :
Now I can see why, but in my case I have a boiler pump and a CH pump -
reason is that I have a wood burner with a back boiler, and the oil boiler
and its pump go off when the wood burner is hot. The wood burner piping is
open vented without disruption but the boiler pump has isolator valves either
side of it for replacement - I had to do that last year and I would have had
to drain down most of the system if the valves weren't there.

Is there a solution to this or is this the boiler manufacturer protecting
himself?

My single pump for HW + CH in an open vented system has isolation
valves either side of the pump too.