I have a G Reg Volvo 440, an in all respects it is behaving well except
for the heater only just manages luke warm air at any time

After starting with the heater on full with the fan on any position the
air coming out is cold as expected but it never gets above slightly
warm, certainly never hot as I would expect. the engine temp seems to
be good about midway on the guage when heated up.

I did have a leak in the radiator during the summer which got fixed
with rad weld, could this have caused a problem ? also the air flow in
addition to not being hot is very low, vastly improved by moving the
temp controll to cold, could the heater matrix be full of dust on the
air side, if so how easy is it to get out and clean

Thanks in advance for any assistance

Phil