I think the CF45 is a quick recovery cylinder. I don't know how your system is setup, but if you have a priority system, so that the boiler sends all its heat to the cylinder, and install a blending valve on the DHW draw-off, and the up the storage temp to 70-80C, you will find that the little cylinder will perform no problem at all and give bath after bath. It will also give a nice long shower too. If you had a 25kW and above boiler, it will perform even better, as the larger boiler pumps in heat as you are extracting it. Combines the energy of the cylinder and the boiler. Using a probe cylidner stat is better as the stat reacts faster and brings in the boiler quicker.