I have just re-routed a radiator, not far but had to go up and over a door. It just won’t get hot, I’ve bled and bled to no avail any clues?

mermeliz is correct. You can buy automatic venting valves that work very well. The beauty of them is they will vent air as it arrives. See link for example. Swap the first elbow for a tee and include a short lentgth of 15mm tube to fit the air vent.

radiator has an embolus of air

. . . . in other words, you must be able to bleed the pipes at the highest point in the system: that's where the air goes.

There has to be a suction pump on the return line.

Up over a door way? I'm thinking you need to vent that section.

So what is meant by "to no avail"?

Have you re-pressurised the system?

Have you opened the valves to the moved radiator?

is there air escaping, water escaping or nothing?

Are you trying this with pump running, or system switched off?

You need to put a bleeder valve at the top of the feed pipe as it goes over the top of the door. Air is getting trapped on that uphill side elbow!