Whining noise on boiler when it starts up from cold?

I have a Ideal Classic RS250 basic boiler (no fan) when it strikes up from cold it gives a loud whining noise for about 5seconds then again for about 5 more seconds then nothing at all. All rads are working and the hot water is ok. Both pumps are working ok . The noise is definitely in the boiler. Any suggestions? Not long been serviced