2 Year old radiator rusting and cracking

Corrosion could be caused by a small weep of water, or Radiator may have been poorly prepared and painted, check for moisture, eliminate leak , treat rust and prepare prime and repaint.

blank not sealed properly and has caused this,or you may have a rad made to a poor standard.

You have a small leak from the screw cap. And the crackling is the expansion of air bubbles.

There are two possibilitys here. One is that the blanking cap has developed a small weep over time. Not enough to notice water running out, Maybe only when the heating is on and the radiator is at its hottest. Please note, the following should not be carried out with the heating on. You could shut the radiator valves, bleed out any pressure within the radiator via the bleed valve on the oppersite side. Then you will be able to safely remove the blanking cap. This will allow you to treat the surface rust and re-paint the effected area of the radiator. Ensuring the rubber O ring is in good order, you can replace the blanking cap. However, in this instance. It would be good practice to replace this O ring. Any goog plumbing supplier will be able to help you with this. The second out come is that the radiator is poorly made and rusted from inside out. Possibly, the radiator has been hit in transit before fitting and caused damage to this area. The only outcome here is to replace the radiator. I hope this helps.