Boiler Knocking noise

[UncleZen]

Its a fairly old (27 years) Potterton Flamingo II. Its been as good as gold. Serviced every 2 years.
Just lately its taken to making some knocking noises whilst its "on", if anything they sound more like loud expansion noises. I don't recall them before.
Should I be concerned? Should I get the service guy in?

Cheers

[digitaria]

The symptoms suggest a build-up of scale in the boiler heat exchanger. You could try the introduction of some X200 (http://www.screwfix.com/p/sentinel-x200 ... 1ltr/43140) or an equivalent, if you're confident in dosing the system yourself. People with similar issues have reported positive results.

[88V8]

And then (hobby horse warning) make sure there is sufficient water treatment in the system to prevent further scaling.

V8