Fireplaces and Chimneys

[Dead Eye]

In my parents house, there is a multi-fuel burning fire that is typically fed with wood however there is recent concern about the build up of tar in the chimney flue which can cause chimney fires. I've done a little research about the best way to get rid of these deposits as they are sticky and can't be removed with a chimney sweep.

A couple of products have shown up as special chemical logs which turn the sticky tar into a brittle compound that breaks up. Other places have recommended burning smokeless fuels for a while as the sulphur released does a similar thing. My question really is has anyone had experience with either options or any further advice on how to get rid of tar from a chimney?

Its been in place for years and years, but recently we've switched our fuel source and this may be the cause of the larger / faster tar build-up. Unfortunately as this fuel is currently completely free its not ideal to switch from using it. Its compressed briquettes of saw dust that comes from a joinery business owned by family friends, although its not 100% clear as to whether this is the cause - its just something that was mentioned by the person who came out to sweep the chimney.