plumbertony

If you are happy to keep the controls as is a new boiler could (without looking) be connected to to the end of the primaries and minor wiring alterations would make it all work. Assuming you have gas, condensing boilers all have anti-cycle timers internally and are also modulating to heat load anyway.

Probably best to change anyway it looks awful.

Maybe too late, the nuts on gate valve type pump unions are slotted so they can be removed over the flange. By cutting the old nut through the flats and prying off the pump carefully so as not to damage the face the pump and nut can be replaced without changing the valve. Hope this makes sense and helps.