The radiators (towel rad + radiator) in my loft conversion won't heat up. I have an S plan system and an megaflo next to the boiler in the ground floor garage. 5 Zone valves. Each zone in 22mm and 15mm to each rad. Ground floor 1st floor 2nd floor Megaflo UFH When all valves are open the loft rads stay cold. The only way I can get the loft rads to work is by closing all valves and only opening the 2nd floor zone valve then they work perfectly. I've tried balancing and even turning off rads in unused rooms but still no luck. Any help greatly appreciated. 1.5 bar pressure.
It's 22mm flow/return and 15mm tee to each of the two rads. The it is a Worcester junior 28i Combi.do you think the pump could be undersized/faulty?