why is red light coming on?

i have a simmaler problem with my vorkera compact he25 after cleaning out the venturi tubes ,draining the sistem refilling and reducing the hw temp it seems to be running with out the red light coming on but i am not convinced that it is running the way that it should be. Going to look at a few more options of wich one might be the theromastats, over heating problem possibly. i did have a previous problem with the boler not firering up and it only worked with the inspection cover removed,i am not tonka registard (lol) but this is a no no do not try this at home.i have also have had hot water problems relating to the red light Sorry if i havent be helpfull but i know the frustration of a boiler that doesnot work

Jack of all Master of non
March 2012