Hi I have a radiator that had an original Drayton TRV fitted many, many year ago. The valve itself seized up and wouldn't open any more so I bought a new TRV 4 complete with valve. Fitted no problem. Problem is the old TRV had the room comfortable set to 3. The TRV 4 seems to need setting to 5 before it achieves the same level, leaving only MAX left. Anything below 5 and there's no flow at all even when the room is chilly. There is flow below 5 first thing in the morning when the room is quite cold but it soon shuts down. I have checked the valve itself and there seems to be full movement up and down of the 'spindle'. There is unrestricted air flow around the TRV. Is there an adjustment that I can make or is it faulty? Thanks in anticipation.