I condemned a gas furnace, another tech tested it good...

[pageyjim]

So do you guys condemn heat exchangers strictly on combustion analysis, or do you use that as the first step, then do a visual to confirm?

Both can be done separate or together.

On the example we have here there isn't enough info yet to condemn the furnace. High CO or above 400ppm has to be corrected or shut down. That can be done many ways from cleaning burners and or adjusting gas pressure or the burners themselves. High CO doesn't mean you have a failed heat exchanger of course. Rising CO even under 400 should also be corrected. It should remain steady. Most are easy to fix even with a shot of nitrogen.
Many analyzers have a hx test mode on them. Basically if you have rising O2 after the fan comes comes on is indicative of a failed hx. Many homeowners will think this is akin to voodoo or something so it is good practice to look for the crack especially if it is easy to do so like on the furnace pictured in this thread. I have found failed hx'ers in minutes but spent much longer looking for a crack to be prepared to have an exchange with the homeowner. Many techs don't know CA so don't expect a homeowner to.
Besides visual inspections I have used water tests and there is an easy test to perform using a digital manometer with an induced furnace.
I have never had to shut down a furnace because of high CO unless a chamber was clogged with soot and the homeowner did not want the expense to attempt a repair. I have resolved high CO hundreds of times. Now I am sure it can and does happen but have never seen it personally. On this call clean the burner and maybe try to adjust how it is seated and there may well have been room to adjust the gas pressure with the O2 at 7.6 if I remember correctly. Not saying this wasn't done but I don't know just showing an example.

[vstech]

The O2 was at 7.6 on that chamber, the others were around 11
I was performing a check for a home buyer, and the age of the system, the high CO, on that burner only, and the overall condition of the equipment I shut it down.
Disassembly of equipment falls outside of my diagnostic charge, and its on the buyers agent to authorize further tests.

But, WOW! I find it hard to believe any tech would override a lockout from those readings.

[BNME8EZ]

Interesting, I don’t remember ever seeing that high of CO with that high of O2.

[pageyjim]

Tough spot to be in but I would think that pulling out a ribbon burner a wire brush and a shot or two of nitrogen is worth a shot before shutting down a furnace. JS. At least making the recommendation to do so. For younger and newer techs I wouldn't suggest saying age and overall condition as a reason to shut down a furnace to be included. Be as precise as possible as there are very few reasons to shut down a furnace. Even when recommending an upgrade my suggestion would be to avoid that wording. Don't use age say efficiency or cost to operate etc.

[kdean1]

The O2 was at 7.6 on that chamber, the others were around 11
I was performing a check for a home buyer, and the age of the system, the high CO, on that burner only, and the overall condition of the equipment I shut it down.
Disassembly of equipment falls outside of my diagnostic charge, and its on the buyers agent to authorize further tests.

But, WOW! I find it hard to believe any tech would override a lockout from those readings.

It was clear from the picture from the other tech that he was ignorant of how to use a CA.

[CircusEnvy]

Customers and their obsessions with wanting to save money, but don’t mind sending 50% of their dollars spent on fuel straight out the flue pipe and risk dying in their sleep. Usually in those instances with equipment way past it’s prime, I ask the customer straight up do you hate money?

[Jim Davis]

I can tell by the burners that is an old Carrier. They were famous for having burners in the wrong alignment for natural gas and their air shutter damper was one of the most dangerous I have ever seen.
Years ago a furnace was inspected for a home buyer and they were told the furnace was dangerous. The people didn't buy the house. The next buyer was not informed of the previous discovery and bought the house, Their two sons died from carbon monoxide a few months after they moved in. I think they settled for 2.9 million dollars. Doesn't really cover the loss of a child!!

[pageyjim]

Best scenario here is that the prospective buyer here who sent the OP buys the house and either deals with the furnace on their own or a deal is struck between the buyer and seller to do so.