ONE more VERY IMPORTANT point.
Please check my video http://my.ku6.com/watch?v=27SmiI-BP2...gBvAPw..#share
I mount my fan 10mm or less than 0.5" away from wall of burner.
This gap is BIG ENOUGH for fresh air to bypass to environmental instead of to enter burner if grate is blocked. That is my fan can not create higher pressure inside the burner.
If grate is blocked, due to low air pressure, fresh air can not enter the burner, fire will die. If any flamble gas produced inside the burner, due to the fresh air pressure blown to burner is very low, the flamble gas will escape downward ( due to positive pressure inside the fue bin) to burning pot and burning there.
Uk questions my explaination and asks me difference of my control system and his system, this must be the main difference. "too big blower, no gap in air inlet"