cold radiator puzzle

[Boxerman]

My bathroom radiator/towel rail has stopped getting hot, it's worked happily since installed 1 year ago and has standard non-trv valves. I've bled the rad until I eventually get hot water into it which took 15 mins or so but then it just goes cold again. I've also turned all the other rads in the house off to try and see if it was an airlock that I could force through but still no joy. Had the valves off last night and there's nothing obviously up with them either.

The rad is the highest in the system (gravity).

Puzzled, any thoughts?

 

[D_Hailsham]

I've bled the rad until I eventually get hot water into it which took 15 mins or so but then it just goes cold again.

Are you saying that the rad is full of air which takes 15 mins to remove? How are you bleeding the rad? It should be done with the boiler off, water cold and pump not running. You should also set any motorized valves to Manual, so they are open.

The rad is the highest in the system (gravity).

Do you mean that you have a F/E tank in the loft? Presumably you have a pump (Grundfos, Wilo etc) circulating the water through the rads, so the fact that the rad is the highest is irrelevant.

Have you changed the pump setting - even accidentally?
Is the pipe going into the rad hot?
Have you made any other changes since installing the bathroom rad?

 

[Boxerman]

I've bled water through until it's hot, no air in the system.

I do have a tank in the loft, seems to be working as it should.

Pipes to valves also are cold, not changed anything in the past 2 months, prior to that I had removed a radiator but that shouldn't have affected anything.

 

[Boxerman]

The ongoing cold rad saga has taken a strange twist, it seems to work randomly about 1 day in 5 or so however I've recently noticed that it always comes on when the bath is run (when heating is also on) Can't think of any reason why this would affect the radiator, any thoughts?