New boiler advice, standard or combi

[camerart]

Found it on the web, and efficiency about 79%, whereas modern boilers are more like 95%. But it would take a long while to get into profit if only changing it for that reason.
Another thing is, with no motorised valves, can only work in HW only mode (power to boiler but not pump), or HW + CH mode (power to both). In HW mode, even when the cylinder is hot, the boiler goes On/Off on its control-stat, using gas, and it soon loses heat up the flue between cycles. So if you want HW always available, to avoid too much waste, need to set the HW time right, manually or by timer (if you have one).
You could improve efficiency by converting to Honeywell C-plan, by addition of a motorised valve and a cylinder stat, without great expense. There's information on the web.
Edit - I suppose you have a roomstat?

Hi F,
I've just worked out the inefficiency! I pay approx £300/year extra. In the winter it's on all day.
C.