Exhaust Elbow corroded and leaking

[UFOboater]

I have a T90 with Bowman heat exchanger. Between the Bowman and the exhaust elbow is an adaptor. The only clue as to this part is from ASAP supplies who provide an exhaust adaptor
with 81mm PCD flange increasing to 98mm PCD flange. They say this replaces Thorneycroft part no. 54009185. My issue is that the elbow has cracked and I wish to replace it with the same (or same sized flange and outlet pipe). Does anyone know the reason for this exhaust adaptor and to which exhaust elbows it was designed to be compatible?

 

[Miss Business]

How do you check an exhaust elbow to determine if it is working properly?

 

[TQA]

How do you check an exhaust elbow to determine if it is working properly?

Take it off and inspect the interior. For some reason they block up with carbon and scale.

Boil it in kettle de scaler or brick cleaner.

 

[Miss Business]

Thanks