Single radiator in bathroom not working

[DIYNovice1979]

I recently moved home and found the radiator in the ensuite shower doesn't work, according to the previous owners it has never worked and a plumber said it'd be a big job to fix. Being the inquisitive type, I thought I'd have a look at this. All other radiators in the house work fine. There's no air in the radiator - when I opened it with a bleed key, water came out straight away. The thermostatic valve is open all the way, I've even removed the valve head and tried pushing the pins in - they move freely.

Going a step further, I decided to loosen the bottom nuts to see if water comes out of both sides, it does. A plumber mentioned that replacing the valves could get the radiator working again. I have 2 questions:

1. If the pipes at the bottom of the radiator don't get hot why would replacing the valves help?
2. The nuts came loose quite easily, but now when I tighten them back up, they still leak (very small drips). I'm tempted to tighten them more, but I don't want to over tighten and possibly make a manageable leak a lot worse. Am I being too cautious?

Thanks

 

[Wayners]

Maybe an isolator was switched off so you only have water flowing in front one side?

 

[DIYNovice1979]

Silly question, how do I find the isolator? What’s it look like?

 

[CountryFan]

Could be a balancing issue, or that lockshield valve (non thermostatic one) on the right could be closed?

 

[DIYNovice1979]

Got the valves replaced, radiator warms up nicely now

Although, I still don't really understand why the feed pipe underneath didn't warm up

 

[ChrisJP]

If the old valves were blocked and stopping the flow, then the feed pipes wouldn't get warm either, because there's no flow of hot water through them.