When to flush a central heating system? All aspects of plumbing questions and answers, help, tips and information

[Gene12]

Our central heating system is 6 years old and apart from a recent problem with an intermitant vibration in the hot water pipe (see earlier question - any help would be appreciated) works fine. My question is should the central heating system be cleansed, drained and refilled after a certain period. When I last bled the rads a little the water seemed pretty clear.

Thanks