Should a hole develop in the tip of a thermocouple after it is installed in a gas heater and lighted

This is an edited answer

After reviewing the additional information provided above along with relevant information obtained from this post: What is wrong with my gas furnace? I have entered my answer below.

The "something red hot" in your furnace is apparently a "hot surface ignitor". The red hot glow is produced by passing current through the ignitor and is the intended function.

Now, to my concern for your safety:

I originally stated that there did not appear to be a thermocouple on your furnace. While I maintain that there is indeed no thermocouple, I also add that the hot surface ignitor is likely monitored by the control module in the furnace. While I am not intimately familiar with this furnace nor the application of such an ignitor, I can safely presume that the control module senses the resistance of the ignitor and can tell this way whether the pilot light is lit or not.

One way to verify my assumption about the control of gas flow would be to remove the connector for the ignitor while the unit is off and then see if you can hear the gas flowing (or can otherwise sense the gas flow - temperature, smell) when a demand for heat is made. Just make sure you do this quickly and safely! (i.e. Do not reconnect the ignitor unless the thermostat is off!!!)

It sounds to me like a restriction at the regulator, not the control valve. You mentioned that the previous owner had done some work on it, make sure that he/she did not replace the regulator with one that does not deliver the design flow/pressure. In this case, adequate flow/pressure depends on proper regulator back pressure setting (they are rated in "inches of water" back pressure). If the regulator setting is too low, it will not deliver an adequate flow/pressure of gas.

If this is the case, the initial proper operation followed by diminishing performance is explained by the volume of gas in the 8' tall hose assembly, with a slow reduction in adequate volume being delivered by the undersized regulator. I had your exact problem when I attempted to swap out a leaky patio heater regulator with a BBQ regulator that had a different pressure setting.

Like this:

• Regulator is initially open because of low (zero) downstream pressure.
• 8' tall hose fills with gas until rated back pressure downstream of regulator is reached, regulator closes.
• You open control valve and light heater, regulator opens as downstream pressure drops.
• Damaged, defective, clogged, or undersized regulator cannot supply enough gas to maintain proper flame height as pressure drops, but does stay open and deliver gas according to it's pressure setting, which is not enough for adequate flame propagation.

It's worth checking, anyway.