They are used a lot in CH systems - are they unreliable?With the greatest of respect for BAS's suggestion, why not just make up a by-pass for the pump and install a NRV, the water wil take the easiest route and almost rule out a potential failure of a motorised valve if you fit a timer.
But your idea would be cheaper. Would it work OK when the pump was running? The NRV would stop any back-pressure problems, but would you still get some flow bypassing the pump?