You'll obviously have found the manuals when you did the search to help yourself. In case you missed them, the installation, fault finding and servicing manual is here (check pages 25-30), plus users manual and a technical document
http://www.sabreboilers.co.uk/sabrehe.html
That should be enough to tell you what the red lamp signifies and a fault flow chart.
Obviously, you'll be asking a certified Gas Safe engineer to work on the boiler.
You may find other prople have had a siumilar problem - a further Google search may help
Anon, November 2016
