Talk to me HVAC guys. I have a Modine 100000 BTU heater, ductless in my shop. The standing pilot won't stay lit. Getting 27.2 millivolt at the thermocouple when I hold the red button in and relight my heater. Getting ~28 volts at the gas valve when I turn the thermostat up, thus indicating the safety switches are not tripped (they are in series with the gas valve on the wiring diagram). What else is there that could be bad? I tried a new thermocouple for 11$ sh1tz and giggles, no go, which I suspected would be the case with the reading I got. I don't want to spend a couple hundred on a gas valve if I do not have to, but what else could it be?