Ouch

Yikes thats Highway robbery!

Not to mention that who ever put in the boiler & piping did it all wrong & to get it redone correctly its $14k

I won't leave without payment on an after hours no heat call. I've pulled parts back out before. Been burned too many times.

Ps scratching a flame sensor won't hurt it. Might cause it to get dirty faster, but it will work fine no matter what you clean it with.

If you scratch the flame rod with sandpaper, you will change the ratio of 1:4, therefore the rectified flame signal will not be correct when it returns to the module and the furnace will lock out because it cannot prove flame. So, scratching the flame rod does make a difference, and I have no idea how scratching it would make it get dirtier faster.
Just my 2 cents.

Well FWIW, in my defense, when I suggested sandpaper, in my mind I was suggesting the black sandpaper of several-hundred grit like 400 or 600 or something. Admittedly, I didn't actually type it in because it was perfectly clear to ME what I meant and gosh darn it all aren't I a reel gud communicatorator? (Don't answer that plz. It's Christmas. Okthxbai.) Anyhow with that kind of sandpaper you're not going to scratch the metal.

I didn't realize you can burn your furnace out by being too late on replacing the filter. I thought maybe the consequence would have been dusty air or just less air turnover. I've learned something new..

Im not trying to be an ass Tony, i hope thats not what came across. I was just trying to state that using sandpaper is not a good idea.
To have someone say it won't do anything to the rod is just wrong, and it will have to be another component that will have to be replaced at the customers expense. In my opinion, poor advice.
Thats the problem with posting, you can read into it.