Should I get radiators and boiler power flushed (as lots of grunge)?

As a rule of thumb, sludge is heavy, being dissolved rust suspended in your heating circuit and wants to settle at the lowest point, which is normally the ground floor area basement radiators. If there are several radiators that feel much colder then the first floor radiators, this is a sure sign of heavy sludge deposits, then the most effective solution would be to power flush the entire heating system including your boiler. A standard 3 bedroom property with 8-10 radiators takes me a full day, so expect to pay a full day's labour rate plus chemicals. NB: Whoever carries the power flush out, ask them to provide a 12 month certificate to guarantee their work, if they are a little elusive, show them the door.

Short answer is Yes. Make sure you use a professional plumbing & heating engineer.