Slugbabydotcom
Thanks, you have confirmed what I've thought was going on. Thankfully the installers have not signed off the work. So I can get them to check it.
ollski
FYI - I had my boiler and cylinder replaced. The old one was the original when house was built!! No idea about the Y or S...
I'm having the excat same problem. Just had our old boiler replaced with a Potterton Suprima 60HE. Since it has been installed, the downstairs rads have been constantly hot. There is no way of switching them off!! I put the programmer on off for both HW and CH. Thermostat at 16C. Still the rad...