Mattm that is new to me. Go on.....
Got it in one! V Good!.
Only when a serious amount of heat is depleted which takes a time as two stats are used. When burning, the boiler is at optimum conditions.
It does NOT cycle. It re-heat the cylinder and only comes back when the cylinder is depletes.
Matt, you are learning . V Good.
Matt, none exist as none go from 0.1 kW to max kW. Modulating boilers are less efficient than fixed rate burners which are optimised for maximum efficiency.