I have been reading some old posts on various forums and the general line seems to be that with room sealed (balanced flue) non-fanned boilers you only do a case-seal visual inspection, not a spillage test with smoke etc. The installion (not servicing) instructions for the Ideal Concord WRS240 state:- "Check there is no spillage of combustion products from the boiler draught diverter by carrying out a spillage test as detailed in BS.5440:1." Any views how this could have been done (back in 1979) ?