Hi everyone looking for advice,today I changed a bathroom radiator for a towel radiator,it is a pressurised combi system,I switched off power to boiler and drained down system,the pipework is 8mm copper microbore,I used two 15mm to 8mm reducers then plastic pipe and connections to towel rail .,before repressurising system I poured in inhibiter directly into towel rail.I have bled all rads and they are all hot except for the new towel rad .I don't think it is anything to do with new valves because the pipework to the towel rail is not hot,could this be some kind of airlock?any suggestions will be greatly appreciated,cheers