mcmoby69

flue is made up of two pipes(coaxial)where the inner pipe fits into the plastic terminal ther is a rubber o' ring. i have had a factory assembled flue 'pinch' this o ring. it caused the condensate from the flue gases to leak into the outer f pipe(air intake)and because condensing boiler flues should be angled upward the condenste runs into the combustion chamber. the technician should look in the space between the two pipes for water . if there is he should check this o ring seal. if it is this it will be intermittent because the boiler is not always in condense mode.the water could be dripping onto sensors etc.