Trane furnace HX crack

[ajk]

Hi - my furnace was trying to come on but would just turn on and then turn off right away. This kept happening and the furnace would not stay on - it was just cycling. The house temperature dropped, so I called Enercare. The tech came and did not do any cleaning or do any tests using any instruments. He just shined a light in the HX and told me there's a crack in the primary HX and I need to replace the furnace as I could have CO leaking into the house. He red tagged it and gave me a number at Enercare to get quotes for the furnace. I thought there had to be a proper combustion analysis done before red tagging a furnace?

I called another guy to check furnace and he told me he can't find any crack in HX. The flue vent carbon monoxide measurement was 20ppm at the 3" pipe. Is this acceptable?
From what I've been reading CO level below 100ppm in furnace flue vent is acceptable.

I ended up cleaning the flame sensor myself. Any reliable tech that'll do a proper combustion test etc?

Thanks

[tenletters]

The only company I trust less than Enercare is Reliance. You're better off calling your dentist to work on your furnace. He at least will tell you he's clueless instead of purposely trying to rip you off.

20ppm CO is perfectly fine, although I have found cracks with good CO level readings in the past.

Most techs still use the standard CO reading in Canada. COAF is a better measurement as it is the undiluted CO amount. I normally go for under 30 COAF. You're probably somewhere around 30 - 35ppm COAF.

Also, there does not have to be a combustion analysis done before tagging a furnace.

[ajk]

Thanks for the info tenletters! 
I've learned my lesson - not to call Enercare or Reliance.
The furnace manual says the HX is under warranty for 20 years, the furnace is 15 years old.
The burner flame is solid blue, I didn't see any yellow or the flame moving around. I hope to find a trustworthy local tech in Vaughan for regular maintenance.

[walker]

Enercare and Reliance technicians are paid commission and are taught to get sales leads, they have no interest in fixing any furnace.