Hayward H250 Burner not lighting

[robrotter]

I have a Hayward H250 pool heater millivolt system, the pilot lights fine and stays on with a nice flame but I cannot get my burners to fire. My thermopile has an output of around 650 MV so that should be enough to open up the gas valve I thought. I have checked the continuity of all safety switches, they are all closed. I have jumpered each single safety/control and nothing has fired the burner. The only time I am able to fire the burner is when I jumper the TH and TH/PP terminals, but once the jumper is removed the burner shuts off along with the gas valve. I have follwed all the troubleshooting in the manual to a tea and am now on the step where it tells me to call Hayward Technical Service. Thought I'd just hop on here and see if anyone has any suggestions. I have heard that small amounts of dirt, or corroded contacts could be the source of the problem since the voltage is so small going through each component but I cleaned everything up and am still at the same spot.
Any help would be appreciated

 

[Insomnix]

I'm taking to check continuity, you have connected one terminal to the side of the flame-out and then turned up the thermostat. From here, bringing the other probe around to the pressure switch, thermostat, hi-limit, lo-limit, and other safeties. When checking the wire to the gas valve, you should still get continuity. 650mv is enough to engage the valve, and if it goes off when you jump the valve out, it sounds like a safety issue. Also, as you stated, if you have dirty terminals or corroded, it will reduce the resistance and not allow enough power to get to the valve. Another thing to try. Turn it on and check the voltage from ground to the valve. See if enough voltage is making it around.