Flame rods or ionization probes fail?

[Neosec]

I read a post by op9 regarding the theory of operation of Flame rods or ionization probes from back in July of 2007 -

http://www.eng-tips.com/viewthread.cfm?qid=163477

which was very informative. My question is, can a flame rods or ionization probes go bad? Are there any active parts in them that fail? My understanding is that these are simply a metal rod usually Kanthal (iron-chromium-aluminium). Am I correct that a build-up of foreign deposits that would reduce conductivity could be cleaned off with emery cloth? Other than that failures would be physical. Failure of the insulation required for mounting or failure of the terminal connection for the electrical wire. Right? I was speaking with an HVAC guy that said they do go bad... I wondered, how do they go bad?
Thanks in advance.

Chuck

 

[MintJulep]

Loss of insulation between the rod and "ground" is probably the most common failure mode.

This can occur from soot build-up on the insulator, or from various cleaning fluids or other liquids wicking in between the rod and insulator.

 

[Neosec]

That's what I thought. Thank you for the reply!

Chuck

 

[danw2]

A couple other failure modes:

AC excitation supply voltage too low

Condensed moisture on flame rod when cold reduces area, signal too low

Rich, yellow flame is insufficently conductive, DC current too low

Flame rod made from coat hanger wire, brake tubing or welding rod will tend to fail is much shorter time than one made of Kanthal.

 

[MintJulep]

Dan,

All of those failure modes are easily overcome by pushing in the flame safety relay and jamming it closed with a tiewrap.

 

[Neosec]

Ha ha ha Mint, you a funny guy! Safety relay? Engineers always use too many screws and way more parts than needed. I often put thing back together with a bunch of parts left over and they work just fine. ;-)

 

[danw2]

MintJulep's humor is sardonic (mocking or cynical) and I love it.