is my boiler working right?

i have a potterton prima b boiler at home which seems to take forever to get the house up to the desired temperature. when the call for central heating is on it fires up the boiler but after a while the boiler just returns to only having the pilot light even though the call for heat is still present, after a few minutes it fires back up but it seems to repeat the same sequence all the time. i dont know if this is connected to the problem but there is a banging noise from the boiler when it is running. any advice would be greatly appreciated.