If the pilot light goes out, all the gas to the device should be shut off. This usually only happens if the gas supply is interrupted, or if you deliberately shut the device completely off.

The device may think the gas has been shut off, and turn off the supply, if the pilot light is blown out by a wind gust (or when you try to clear the dust inside with the vacuum cleaner) or if the thermocouple that detects the heat from the pilot flame fails.

The thermocouple may be what looks like a little metal rod just above where the pilot flame should be, or may be a short coil of what looks like a fairly heavy steel or copper wire. (The "rod" form is much more common now, at least here.)

In order to get enough gas to re-light the pilot flame, you must override (bypass) the main shutoff valve, either by pushing and holding a button (nearly always a red button, sometimes in the middle of the knob used to turn the main flow on/off) or by turning the main control knob past the normal operating position.

If the pilot override is on the main knob, the position you must turn the knob to will likely be labelled as "pilot," or "light" or something similar. The knob should be spring loaded to snap back to the normal operating position, so IF YOU RELEASE THE KNOB (or the button if that's what you have) the gas will be shut off and the pilot flame can't be lit.

Once there is gas flowing to the pilot flame burner, some source of ignition must be supplied. In older devices, you might have to stick a match in. Most newer things (here at least) probably have a piezo igniter that produces a spark or series of sparks. A very few devices here have recently used a system that turns on a "stream of sparks" (like an auto spark plug) when the pilot gas control is moved to turn the pilot light gas on, sometimes powered off the thermostat transformer but usually from the blower fan line.

A piezo igniter usually must be actuated by pushing a button or sometimes by turning a separate knob. Each push on the button produces a single burst of sparks, so if the pilot flame doesn't light you need to push again, repeatedly, until it does.

In some devices the piezo igniter is operated by a knob that turns for a little ways up to what feels like a detent, and when you turn it through the detent position a spark is produced. Again, if the pilot flame doesn't appear at the first detent, you need to keep turning through successive detents until there's a flame. (This may be more common on propane stuff than with natural gas?)

ALL OF THE TIME while you're operating the igniter, you MUST continue to hold the pilot light gas button or knob. The igniter can't accomplish anything if there's no gas flowing to the pilot burner. (This isn't usually as hard as it sounds.)

You must continue to hold the gas button/knob until the thermocouple heats up enough to keep the pilot flame burning when you release the button/knob. With some units, this means holding the button until the main burner comes on. (But note that the main burner won't come on if the thermostat on the wall is set below room temperature, so you might want to crank the thermostat up a few degrees before starting to re-light the pilot just to be sure - but don't forget to turn it back down before you bake yourself.)

Most larger heaters can be installed in a number of different configurations, but it is the responsibility of the installer to make sure that the data and instruction plate matches what is installed. Where the label says you have a button, you should find a button. If a knob is indicated there should be a knob. It must always be considered, if something doesn't work as indicated that the installation was done by F***up Engineering Co LLC and they put the wrong instruction plate on, or they recycled a used unit and changed something.

John