h400ed2

Heater starts for 2-3 seconds, I can see the flames, then the heater shuts off. If I cycle thru the standby/spa/pool settings then I can get it working for 15-20 seconds max. Orifices are clean. I measured 22V on the valve. My heater doesn't have flame sensor (I wasn't able to find it). Any ideas?

Just fired up the heater [Hayward H400ED2] for the first time this season and boy did it make a racket! Pipes were bouncing around and it sounded like an animal was stuck inside trying to get out. Poking around on the internet, it seems like it's likely the thermocouple valve. The heater is...