I having some trouble with my Hayward H250 millivolt heater. It worked the first day the pool was opened, about 3 weeks ago, but I haven't turned it on since I tried again yesterday. The pilot is on but the main burner won't come on. I turn the switch to "on" and turn up the thermostat but nothing happens. I don't hear anything. I have a manual and it says I can jumper the "TH" terminals on the gas valve and then work my way through the pressure switch, thermostat, etc. Is this the first steps I should take then? Are there any other things I can check first? There is some corrosion on the terminals at the gas valve. I'll try to clean those up.