TRV problem

Are you sure that the valve is on the correct side of the radiator, with regard to flow and return? Unless it's a bi-directional valve, the water

If the TRV is fitted the wrong way round the room simply gets hotter and hotter... been there and cooked until I worked out what I had done.

Does your radiator get cooler as the room warms up or does it simply stay hot all the time? If it stays hot all the time without the room getting any warmer it probably doesn't have the capacity for the room requirements.

Is there a reasonable temperature drop across the rad?

Peter

If the radiator gets hot, but the room doesn't, it doesn't suggest the TRV is faulty.

It is more likely that the radiator is too small for the room, particularly if it is well ventilated. Alternatively, the system needs balancing because the radiator doesn't get hot enough.

Christian.

Is the bathroom radiator connected to the circuit that heats the stored hot water?

If so, is it gravity circulation or fully pumped to the hot water storage cylinder?

TRVs won't work well with gravity ciculation, the gravity differential pressure won't produce sufficient flow-rate due to the TRVs resistance, causing problems as you describe. I think you can get a special TRV for this application.

I posted this >24hours ago, but it seems to have got lost; apologies if it gets duplicated.