I have a Rheem 21vp50-1: Gas, blower, electic igniter.

It stopped producing hot water yesterday. I think the problem is the
igniter, but wanted to confirm my suspicion before buying an
ignitor.

After turning the heater on/off many times, reading the diagram, and
playing around, this is what happens:

1) turn ON switch
2) blower starts
3) vaccuum switch causes controller to click (disconnecting hose
prevents this)
4) gas valve turns on (won't happen until after #3). I can smell the
gas.
5) a controller clicks follows-I think this is for the igniter.
6) After ~20 seconds, it repeats 3-5, but no spark, glow or flame ever
occurs

It seems like the controller is doing the right thing.
About 1.5 years ago the controller was replaced, but the igniter was
not.

Anyway, I'm not sure how to test the igniter.
Perhaps I'll put a volt meter across the igniter inputs.

Any help is appreciated.

Kitt