Puma 80e downstairs radiators cold upstairs very warm?

Hi i have a Potterton Puma 80e combi boiler. With the central heating on the upstairs radiators are getting very warm and downstairs is cold. I have tried to balance the system and this only seems to reduce heat across working radiators. The boiler is upstairs meaning downstairs rads are furthest away. I have check and the pump is running however it is extremely hot ( wondering if it could be running slow ). Have also noticed that the flame light comes on for around 20 secs then switches off again, it seems to do this every 5 mins or so. Any help would be great as at the present time quite confused.