Thank you, Larry.
Sadly, I forgot to say it’s a Richmond (Rheem) 6RHE40SP, if that helps to know the inside construct of it. We filled it with water and it held water, no leakage. I just didn’t know if the combustion chamber, or whatever they call it, is very susceptible to damaging in such a case.
I understand the thermistor is located in the gas control probe in the water jacket. So, whether that’s replaceable separate from the gas control or not I can’t tell. I can’t seem to find any literature on how to remove the gas control and probe.
Any further suggestions?