I left the whole transducer in a jug 1pt filled it just above the protruding part with the black tip just covered very hot not boiling for 15 mins this has worked twice and worked perfect
three days from after posting it stopped again put the transducer back in a jug with OUST descaler working perfect it seems it will need to be done regular depending on use our fire is used 14hrs a day most days
I had the same problem with the smoke transducer, dimplex sent a new one, because the fire was less than 12 months old. Decided to put the old one in a solution of all purpose descaler ('Oust'). Removed the new transducer, connected in the old one, since then the fire/smoke effect has worked...