Radirators can be very trickey to get working.
Starting by purchasing your waste oil heater with the copper coil fitted.
You need to plumb it up using an Ajax Valve teed on the cold side of the coil, which is the bottom of the coil.
The Ajax valve connects to the town supply water, to keep the loop full of water all the time.
An open vent is needed, extending at least 2 metres above your radiator, this needs to be teed into the hot side of the coil, being the top.
Fill the loop up with the town supply water. Turn the Ajax pressure screw until the water exits out the top of the open vent, then turn it back one turn. Stopping the water from flowing out the vent. This is called the water head.
Next is bleeding the air out of your radiator, until only water exit the bleeding valve at the top end of the radiator.
Light the heater, The heater needs to be running at 400C to heat water around 99-100 degrees C.
If your using a pump turn it on to circulate the water, or you will hear a few bangs if your using the thermosyphon way. This is the noise of the water being pushed up the pipes, it will stop once the water stars moving.
If the bangs carry on, then there will be an airlock in the radiator so bleed it more until only water exits.
If nothing comes out the bleed valve, then the Ajax Valve needs to be turn on further until it does.