Wandering if this might be becasue previously with the forst site www and non-www both worked, and worked with ssl, and these three lines
RewriteEngine on
RewriteCond %{SERVER_NAME} =floheating.co.uk [OR]
RewriteCond %{SERVER_NAME} =www.floheating.co.uk
#RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
work conditionally, upon the last line being un-commented/ enabled