Wonder if anyone can advise please. i've been reading till Im dizzy the fine art of balancing my system and every day I find myself with my digital thermometer re adjusting the flow and return to each rad. Just as I get it absolutly perfect (20 degree c differential), the very next day its circa 12 to 15. Anyway, my heating is brilliant as a result of all the tinkering and works perfectly but being a perfectionist, i've been reading further that my Vaillant EcoTec 630 should have a flow & return temp differential to the boiler of 20 degrees c in order for it to work efficiently and condense. My question rather than problem is how critical is this differential at the boiler given that my system works A1 perfectly and the rads vary in flow & return differential between 12 and 20 degrees but the rooms that need more heat have the lower diff so it actually suite my layout. Any responses greatly appreciated from a perfectionist!!!