Underfloor heating struggles

We moved into a new build earlier in the year with wet ufh and an air source heat pump. We were fine over summer but now the house is struggling maintain 20°c even though the thermostats (set to 23)all show they are calling for heat. Our basement floor is never getting above 18 and I'm worried if the outside temp drops further those rooms won't be usable. Is this a limitation of the system or are there steps I can take to improve it?