Boiler overheating with UFH

[cdb00001]

Good afernoon, I recenlty extended the house and added a small area of UFH to the main heating (radiators) system.
Since the installation, the boiler randomly overheat and shut down. This only happens when the UFH starts, mainly in the mornings and especially if it starts at the same time as the radiators central heating. To avoid, I postponed the start of UFH so it starts once the central heating is already on, but it doesn't always work and sometimes it shut down.
The system is new, the pump is new and the Boiler has 8 y.o., it's Combi Glow-Worm Betacom 3 24c. Someone suggested the manifold is defective or the settings are not correct but I have no idea of how should I make it better.

Any advise is welcome!

Thanks

 

[Jurassicspark]

Check the flow rate to each circuit, especially between the radiators and UFH. If the manifold doesn't have proper flow and return balancing, it can cause the boiler to overheat.