RayV wrote:

This is exactly what is happening, every time an individual zone calls
for heat the 'main' circulator pump kicks on with the boiler as well as
the zone pump. The pressure from the main circulator is enough to lift
the flo-control valves off their seats in every zone.

The biggest problem is my BIL makes Tim 'the tool man' Taylor look like
Tommy Silva. So I can't try things like disconnect the main circulator
and let it run for a few days.

Hmmm. I was just about to suggest exactly that- that the fix might be
as simple as unscrewing the wire nut that secures the hot wire for the
main circulator...