car wont reach normal temp

[colorit]

hi ppl im new to this so I hope im posting this in right place,
ive got a 2000 Passat 1,9 tdi se (115 bhp....engine code atj/ajm)
problem im having is the temp gauge on dash wont hit 90 and heater blows just warm air also I don't seem to get water coming from
engine to heater tank unless I rev it hard, ive changed the water pump,thermostat,cts and rad.
but still no change ive even flushed the system twice and back flushed. so any help you guys can give would be great thanks.