poor performing radiators?

Hi
Just moved into a house and the radiators although they work do not get hot enough and room temperature hovers at around 15/16 degrees (bit of a problem at the moment!). Also there are patches on the radiators that are only warm.

We've switched off some of the radiators in parts of the house we don't really use much so only have 5 radiators on the go.

We have a Potterton ep2001 boiler.

Water gets hot enough although does not get steaming.

Does anyone have any advice about simple steps I can go through to help diagnose the problem before having to call someone out?

Thanks

Steve
December 2008