Fix my Central Heating!!?

I have BAXI Combi 105e running my central heating.
Works fine, however,
The house has 3 floors, with Boiler situated on 2 floor. It then feeds upstairs to loft for 2 x radiators -3rd floor
2 x Radiators & Towel Radiator - 2nd floor, &
3 x Radiators - 1st floor.
Problem
2 & 3 Heat no problem and can be very hot
1 - You would be aswell not having them luke warm.
Have bled constantly & topped up boiler , works a few days then back to luke warm.
Have turned all radiators off, only put on 1st floor, then ran system again, works a few days then back to luke warm.

Anty suggestions?

Texas
January 2009