Radiator brainache

LE_Bore

A new radiator was hanging around in our house while some building work was being done. At some point, it got dented. Probably from me bashing my bonce on it in frustration at it not getting hung. 

Plumber cones in, a trusted chap who has been straight as a die thus far. I ask about the dent and he says he can hang it back to front so the dent doesn't show.  But it has an internal valve with marked in and out connections, says I. Don't fret, he reckons, it will just take 10 mins longer to heat up. 

He hangs the rad, runs the system. It takes maybe 5 mins longer to heat up. But it gets plenty hot. Now, a couple of months later, it's no longer getting hot. In fact it barely gets warm. I have bled it, turned the boiler up to stun, turned down the other rads, etc.  Still no go. Any ideas please, lovely people?

Thanks for reading.

WIAWSNB

Is this a column rad? These are directional, as I found to my cost (actually, I knew it was, but still got my new F and Rs pipes the wrong way around, and had to swap them back at the tees...)
I just don't know if having it reversed will only give the slower heating symptoms your plumber claims, but since your plumber seems clued up, and it did initially work ok, then he would appear to have been correct.
So, what's gone awry? No idea. Could it possibility be that the rubber bung inside was dislodged by it being the wrong way around - ie, pushed by the reverse flow? I don't know, but surely highly unlikely - it must surely be a secure fit?
Or, the fault is with the rad valves. What type are they - is one a TRV? If so, make please - or a photo. Some are one-direction.
Or, the cause is further afield - say an airlock in the pipe. Is your system vented (wee F&E tank) or unvented?

Make and type of rad? Worth a chat with the manufacturer - ask what is the worst that can happen if reverse flowed.

Were new pipes run to this rad? Are they easy to get to? Could they be swapped around if needed?
Another possibility is that your other rads are pinching too much flow, so this one is starved - ie the system needs balancing. You say it still doesn't heat up if other rads are shut off, but have you also tried opening this rad's valves up more? If you tweak them, try and note their starting points so you can return there afterwards.
Do you know the difference between 'control' (eg TRV) and 'lockshield' valves? 

HHarry

If it did work and now doesn’t I’d start with an airlock.

Can you turn the other radiator valves off to try and force the water flow through this one?