what are the cental heating pump speed settings for,are they to do with the heat output of the gas boiler,thanks

Basically they are there to overcome the resistance in the pipework. The setting depends on a number of factors. There is no connection with 'heat output' of the boiler. You don't say if you have a problem or not. Usually there are 3 settings. Rule of thumb is middle setting. If the system has been designed correctly.