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A 10 error indicates a blockage in either the air intake or exhaust. It could also be a problem with the fan. The first thing to check is to look for any blockages
Is this a condensing model (PVC vent)? Do you have an ohm meter?
Ok, this is not a condensing unit. I asked because the only other listed cause for this error is a burner sensor fault which is only installed on condensing units. So the only other possibilities since your sure there's no air intake or exhaust obstruction is an improperly installed condensate collar or clogged fins on the heat exchanger. Did you blow out the heat exchanger too? You need the install manual to check the condensate collar installation. Beyond that you may need to pull the fan to be sure there's nothing in there.
I did some more digging. The service manual says only the condensing units have a burner sensor/thermistor but the ladder diagram for your unit shows a burner thermistor so I'm posting a link to the service manual which will give you details on where to probe to check the thermistor resistance (Page 21 & 35). Ohm reading values are in the table on page 21https://www.rinnai.us/documentation/downloads/100000098_Rev_B.pdf