Just asking for some advice. We have a Vaillant ecomax boiler fitter in 2002. The past week we have had big problems with it. The hot water and Central heating are very temperamental. From looking at the boiler display, the temperature keeps dropping and then the boiler kicks in to raise it but then it drops again, so no hot water...or rarely very hot water and the central heating luke warm at most! We have restarted it many times and topped it up and still showing F23. Any ideas what we can do or what it may be?