When dissolved, weak electrolytes only partially dissociate into ions in a temperature-dependent process. We show herein that such incomplete dissociation yields an enormous thermoelectric response in an electrolyte-filled nanochannel along which a temperature gradient is applied. For this purpose, an extended version of the Nernst-Planck equations is developed that takes into account the temperature-dependent dissociation-association equilibrium. The results indicate that in this way, Seebeck coefficients can be achieved that outperform all previously reported values.