This is not strictly relevant to your problem, but why such a large boiler? Did you have it installed or the previous owner?
The boiler has a max output of 33k for CH and 39kW for DHW. It may have been chosen for the DHW output if there is a high incoming cold water flow rate (15litres/min). This could mean it has too high an output for CH.
You have 14/15 rads which will probably add up to about 21/22kW. (Your data shows a max nF of 27, which is approx 15kW).
The boiler has a max output of 33k for CH and 39kW for DHW. It may have been chosen for the DHW output if there is a high incoming cold water flow rate (15litres/min). This could mean it has too high an output for CH.
You have 14/15 rads which will probably add up to about 21/22kW. (Your data shows a max nF of 27, which is approx 15kW).