The same type in the upstairs bedrooms get very hot, however the new replacements are worse than the old ones as I do not appear to be able to get them even luke warm. It is a standard gas boiler, single zone, vented system, plumbed via two manifolds in 8mm and 10mm copper pipe. I know there is no air in the system but can't think what else it might be! The old recirculation pump was quite worn and a bit noisy so I have replaced that with a new one without any success.