Simply a large bottle of water is suspended some way above the burner unit and a hose attached to the pellet feed tube. The end of hose is sealed with bees wax or a similar low point melting plug. If there should be any back burn, the wax would melt and release the water immediately quenching the fire and preventing any re-ignition. The release of water would not cause any serious damage to the burner or boiler.
Simple ideas are often the best. To me, this appears an elegant solution and would cost very little indeed to implement.
(1) The type of hose pipe to be used,
(2) The method and place to attach the hose,
(3) The type of wax or other heat sensitive sealant utilised,
(4) The quantity of water, and
(5) the height of the water, would all need to be verified by testing.
A retro-fit kit of this type could be produced and sold for very small money. Or will we in Ireland wait until a few homes have been burned down before we act??
SEI please take note!!