A Regular boiler is a heat only boiler, with only components internally required for generating and maintaining heat ie heat exchanger, gas valve, fan, primary flow and return connections, and the main electronics.
This type of boiler requires either a F&E header tank or Sealed Expansion vessel kit and filling loop, external pump, external zones valves and controls.
Heating Controls
In regular boiler heating systems it is very common for an S / Y Plan setup. It is possible depending on the boiler, to have a PDHW setup Priority Domestic Hot Water (PDHW) using the correct controls.
Additional Resources