Looking for a little help on this, it's on vertical flue kit and the emissions are hitting 3000ppm co. I have cleaned the injectors, burner, hx, gas rated ok, bp ok and stripped the flue to check integrety. All is good but the readings are still sky high. I noticed on the inner flue that the female connections seem to have recesses in then to take seals however this one is just siliconed....does anyone know if seals are required or where I could look next?