how do I get hot water on a danesmoor wm 12/19

Insufficient oil getting to the burner due to blocked oil feed because of sludge in the tank, or a blocked jet? When was it last serviced by a competent c/h engineer?

Manual here

Another thought. You mention 'hot water'. Do you mean domestic hot water as opposed to central heating water? If so, and the CH side of things works OK, then the diverter valve (see figs. 12 or 13 in the manual) may not be opening properly onto the DHW side.

Mine's a 15/19 and from a 70's vintage when "space-age" fonts were cool.

Chances are in that era the the hot water is a close coupled convection circuit and so the hot water setting allows the boiler to fire and CH controls the pump to circulate water around the entire system radiators.

Mine gets the hot water hot very quickly when it isn't driving the CH.

Basically something is wrong or the thing was never installed right. IF there are any motorised valves then one of them is stuck.