Review of Esse W35 range cooker
All may not be lost......
We too were driven to despair by our Esse W35 and had decided to ditch it. It struggled to get the oven to even Hot and left lots of unburnt charcoal behind every burn. It was a pain.
I tried one last clean to original new condition and discovered two new requirements: first, the right hand smoke channel needs to be cleaned more than you think. Ours was partly blocked at the rear, its wider than you think. Make sure its squeaky clean right to the back and clear the muck out via the between-the-ovens slot. Secondly, clear the air intake at the left hand base of the firebox. Esse don't even mention this in the manual but there is an air intake down there controlled by the thermostat. Clean out the firebox then undo the L-shaped plate, pull out the lower left firebricks and lift out the perforated steel plate. Clean out any ash until you can see the air opening and the thermostat plate operating behind it. I don't know which of these two operations transformed the stove's operation but it has worked perfectly since: rads warm/hot and oven routinely 175-200 degrees vs 140-150. Give it a try.