TO confirm, yes it is an oil boiler and yes the underfloor is controller by its own mixing set and heatmiser control panel which operates the valves for the 9 underfloor zones. However boiler supply in feeds both underfloor mixing set and y plan for hot water and upstairs rads so twin port valve...
I have a haeting system in an old farmhouse where downstairs is new underfloor heating and upstairs on standard Y plan rads and hot water.
A 2 Honeywell port valve has been added in front of the 3 port valve to shut off when no heat is required for y plan but heat is required for underfloor...