The water heater's hot surface ignitor is designed to give a better performance than the traditional pilot light, and they are becoming popular due to their lack of cost, and the control which they give the user. However, they do need to have the ignition positioned correctly in order to avoid damage.
Step 1 - Check the Water Heater
If you find that the water heater doesn't turn on, then this may be a reason to suspect that the hot surface ignitor is not in the correct place. You may also find that the heater is delayed in coming on, due to the poor placing of the ignitor.
Step 2 - Remove the Ignitor
You should then take the hot surface ignitor out of the water heater, ensuring that you turn off the electricity and water supply, and then unscrewing all of the connections. You may need a wrench to remove the outside surface.
Step 3 - Check the Leads
Lift the hot surface ignitor away from the heater, and check the nozzles are following. You should be able to examine these, and determine if the sensor is able to pick up on the ignitor. The photocell needs to be inside the combustion chamber, if it is not, then this could be the source of the problem.