My name is Jim and I am on my 3rd disco , 2x Tdi latest one Td5. I have a problem with the heating Car takes about 10-15 minutes for heat to come thru , warms up nicely at first then after about 30 minutes all heat goes , does not come back unless Ilet engine cool down and start again.All air bled from system.Thermostat replaced , no change in symptoms .HELP!!!!!!!!!!!!!!