The glowbar is a special carborundum resistor
, used as a heating element to ignite natural gas
Glowbars are common on ovens, clothes dryers, and furnaces. They usually look like a cylindrical or flat steel cage covering a black (or glowing bright orange) double helix structure, about an inch and a half long.
The silicon carbide glowbar behaves as a resistor, and generates heat when electrical power runs through it. It's wired in series with a bimetallic strip located inside the gas valve, which heats and bends when enough current to heat the glowbar also flows through it. When it bends far enough, it opens the valve to start the burner, and the gas is ignited by the glowing hot surface.
The glowbar's resistive element is brittle and subject to cracking. A cracked glowbar will either glow dimly or not at all, and will not allow enough current to flow through the gas valve to turn it on. (This is a great fail-safe mechanism, as the gas won't come on if the glowbar can't get hot enough to ignite it!).
To find out if your appliance isn't lighting up due to a glowbar failure, unplug it, and remove any covers that obscure it from view. Plug the appliance back in, and being careful not to touch any electrical parts, activate it so that it should be trying to light the burner. If all is well, the double helix should heat up to about tangerine orange, and a flame should occur after the gas turns on. If the gas doesn't turn on, check any shutoff valves in line.
To test whether the glowbar's getting power, unplug or turn off the appliance at the electrical panel, remove the wire nuts from the leads to the glowbar, and bend them into a position where the bare wire will not touch anything. Carefully check the wires for voltage after turning the appliance on, using a proper test light or voltmeter. If you see voltage across the glowbar and it isn't glowing, replace it.
Be very careful when handling the glowbar, as the element is very brittle, and the part's kinda expensive.