The greenstar is a decent boiler BUT the parts are hellish expensive if it does go wrong. The brand has dipped a little in recent years. Baxi also still have a very good name in the industry.
Relative new boy on the block is the Ideal Logic. Been out about 5 yr now, we have fitted literally thousands on the old Warmfront scheme and more on the ECO scheme presently. I can honestly say, not been back to one that has been installed correctly
But as with all boilers that is the problem. making sure they are installed to Man Inst.
Of the 30 or so inspections I have carried out this month (Covering from Newcastle upon tyne to Bournemouth) I have awarded only one installation a "clean pass"
Make sure installers pay particular attention on standard boiler installation to cold feed position and expansion position. BUT by far the biggest installation failure is the condense pipe, especially if it is run to an outside drain.
As of a couple of years ago when the majority of boilers with an outside condense pipe froze ( remember that?) then ALL condense pipes that run outside MUST be 32mm minimum dia actually going through the wall to outside
and the 32mm once outside MUST be insulated externally.
Next biggest failure is not to carry out the appropriate flush BEFORE the boiler is fired up, very hard to prove with out water sampling, but you can check for the presence of the protection additive with a simple kit.
Remember failure to install to Man Inst can invalidate your guarantee Warranty providers can and do refuse to honour service agreements if the boiler is not installed to Man inst