I have maintenance contract with gas board for Central heating system but this does not cover flushing out and I believe that this is a costly operation to have gas board do it.My upstairs radiators are very slow to heat up and I think flushing out would help to get better flow.Was thinking of just opening discharge valve and draining out the system and topping it up again,of course releasing air in the radiators at the same time.Can there be any problem in doing this? My system is fully pumped with Baxi Bermuda boiler I would appreciate any help with this .
allan