Yes you can light it with a BBQ type lighter (long enough).
If it lights and stays lit then you need to change the thermocouple (looks like a little pipe off gas valve)
In simplest terms, a thermocouple is a temperature sensor. Normally
inexpensive, a thermocouple is standard on hot water tanks. If your
thermocouple breaks or you feel it is not working properly, consider
rather than installing a new gas hot water heater.
project by shutting off the gas control knob on your hot water heater.
Once you are sure that the gas is off, you should use a wrench to remove
the nut that attaches the thermocouple to the gas hot water tank. This
nut should appear to be securing a piece of copper tubing or other type
of tubing. With the nut removed, you should also pull down on the
tubing, dislodging it from the thermocouple.
Sometimes there is
another nut that attaches the end of the thermocouple to the pilot
bracket, if this is the case you should unscrew this nut as well. You
can slide it down the tubing and keep it there until you need to replace
With the nuts that were holding the unit in place removed,
you should be able to slide the old thermocouple out of the brackets
that hold it to the hot water heater. You should then take it to a
hardware or home improvement store and find a suitable replacement. Then
follow these steps to install the new part and fix the hot water
To change the thermocouple, you should press the end of
the thermocouple into the pilot bracket as far as you can. If you had
to remove a second nut to remove the old thermocouple, now is the time
to replace that nut securely.
With the thermocouple in place,
you should connect the lead to the control unit. Use the nut you removed
in the beginning steps to secure the lead. You should then tighten it
at least a quarter turn with a wench to make sure the lead is securely
attached to the control unit of the gas hot water heater.
that the new thermocouple is installed on your gas hot water heater,
turn on the gas shut off valve that you turned off earlier. You should
be able to relight the pilot and the functionality of your gas hot water
heater should be restored.