Hot Water and Heating taking Hours to heat up

Have had suprima pcb changed 3yrs ago, timer delay pcb 1 year ago, Mixer valve 1 year ago, and pump drive pcb renewed 10 days ago after capacitor buzz, timer clock permanently on, suprima and boilermate at MAX, Problem now is that when called for boiler, as in turning on hall thermostat or running hot water, both are hot for a short period then go cool,before boiler fires up, then takes hours to heat, system 10yr old in soft water area, Thinking now suprima and BM thermostats need replacing, Any Ideas anyone, Thanks.

10 years old.
Could be sludge and or scale.
Also the BM II may be low on water.
Which is the heat source for every thing you want.
Check the small tank and the ball valve.
Next put a hose on the unit and drain some water out.
IF the level in the small top tank does NOT go down then you have a blocked internal cold feed.
Mike
MGC/H2O