Can someone help me understand the specific name and function of the parts directly under the main valve on my old (1987) AO Smith Gas Water heater (with exhaust). There are 2 parts connected together between the main valve and the actual burner. One part is in front and is appx 3″ round shape and about 1″ thick. It has 2 leads from the electrical connector. The second part is behind (and connected to) the round part. It has 4 electrical leads to it. They are connect together. Is one a Gas Pressure Switch ? which one ? I think these parts (or one of them) is not fuctioning and keeping my main burner from working. My pilot light is OK. I bought a pressure switch from AO smith and it is very small but appears to replace the front round part (original 20 year old part).