flue gas bypass?

ken D

This is taken from an older thread:

... I'm not familiar with any commercial equipment...

I do notice more residential types of high efficiency boilers using Direct Spark though, and am trying to learn what aspects of the design will provide the best reliability. Hot surface ignitors seem to be a mystery, even to the people who manufacture them. They can fail in so many ways - internally, where the tip joins the wires (excessive heat), or the tip itself (excessive voltage, cycles, oxidation, FLUE GAS BYPASS).

Flue gas bypass was also used in reference to Lennox Equipment, but what is it?

DaveC

Sounds like something I posted...

awhile back, in the "Equipment Failures" post.

If the flue gasses find their way back into the combustion air intake, it can create many bad effects. Ignitor failure can be one of these - I believe oxidation of the tip would occur, causing heat buildup internally, bubbling, cracking, delayed ignition, etc.. The combustion can also be greatly effected - the air/fuel ratio becomes richened to the point where extreme CO is produced. Corrosion in areas that were not intended to be exposed to flue gasses - air intake piping, combustion blower, metal burner, etc.. Freeze-up at the air intake opening, due to flue gasses condensing and building up ice formation there, too.

This is most common on direct vent appliances, where the air intake is not positioned properly in respect to the flue outlet, or obstruction, wind diverts the gasses toward the air intake. Poorly sealed concentric vent piping can cause the bypass, also. Hope this helps!