# Carbon monoxide formation in broken boilers

It's common knowledge, that if you're boiler is broken, it might produce carbon monoxide ($\ce{CO}$) as a byproduct, which is very toxic, even in small quantities. My question is, why do broken boilers do this?

The combustion of hydrocarbons works as follows:

$\ce{hydrocarbon + O2-> CO + H2O}$

The reaction can then continue to the complete combustion:

$\ce{CO + 1/2 O2-> CO2}$

An example of balanced equation is the combustion of methane:

1. $\ce{CH4 + 3/2O2 -> CO + 2H2O}$
2. $\ce{CO + 1/2O2 -> CO2}$

So, carbon monoxide is a product of the incomplete combustion of a hydrocarbon.

It is produced when there is too much fuel (eg: methane), but not enough oxidant (eg: oxygen from air).

I guess that a boiler which cannot mix properly air and fuel produces carbon monoxide.

• And when/why does the reaction stop at the first stage? – szentsas Aug 7 '16 at 12:10
• It does not really stop at the first step. Both steps will occur but overall there is not enough oxygen to convert everything to carbon dioxide. – SteffX Aug 7 '16 at 14:22