Automatic bypass valve with underfloor heating mixer valve

[Bodgedbuild]

I have almost completed the "wet" side of installing my underfloor heating system up to the point that I have been running it on a low setting, from an air source heat pump to assist in drying my liquid screed floor. So far however, for safety I have also had my radiator zone enabled so that a non TRV radiator can bypass water to the boiler if it is required. What I'm not sure about though is if it actually requires a bypass on the underfloor heating circuit or does the mixing valve on the manifold always flow from and back to the boiler. I sort of understand that a proportion of the water in the underfloor pipes is recirculated if a lower temperature than that provided by the boiler is required but I am unsure if this means that at any point the mixing valve could actually stop flow to an from the boiler? I will also install automatic valves to each circuit at a later date and they will be controlled by individual thermostats so I wonder too if that means the flow could be reduced to an unsafe level for the boiler if they were all to close prior to the main UFH zone valve closing and switching off the contacts for heat request.
Thanks in advance

 

[Bodgedbuild]

Something I have just thought about is that the installer fitted what I believe is a low loss header. Does that negate the requirement for an automatic bypass valve?