I have moved into a house with a dog's breakfast of a CH system. The CH
system looks like it's been around a while, but fairly recently the hot
water tank has been replaced with a combi boiler. (Installed arse about
face as it happens - the TRVs on the (15) rads are all the older type that
are mono-directional - the combi had been connected into the existing
system the wrong way round.)

The towel rail in the bathroom has stopped heating up, but the other rads
are ok. There is no air in any of the rads. I think the system needs a
good clean and then some re-filled with some inhibitor.

The question: Is it a DIY job? None of my DIY books cover it and my
googling of the NG archives hasn't come up with anything definitive in the
Janet and John guide to flushing your system vein.

Dougie