We were called out to a dual fuel boiler that was making “funny” noises. When we checked the boiler and took the fan out we can see the effects wet logs can have on a boiler (tar). Amongst other checks and repairs, the fan needed to be cleaned down, the back of the boiler opened up and the heat exchangers taken out and cleaned. The heat exchangers can be seen in the below picture, through the hole where the fan is normally situated.
Please do not put even 1 wet log in, as it has the same effects on the boiler as all logs being wet.