Sometimes people are reluctance to got to the expense (£40.00!!) of putting access panels into their system.
Obviously it is part of the specification (TR/19) and obviously we need to get into the duct to clean it. What is less obvious is what is in a duct.
See for yourself.
My bet is that this summer this kitchen will be 20 degrees cooler than last summer
There are no magic gizmos, just hard graft, common sense, knowledge and experience