If it works on 120 but not on Gas and everything on the gas side has been checked and it is at spec, then the ONLY thing left is the Baffle. Odds are, there is NO baffle or the Baffle has been burnt up from 27 years of use. Your only recourse is to pull the refer and pull the baffle and see what it looks like. The baffle is a spiral piece of metal and the spiral causes the flame to disburse in a round fashion to correctly heat the bottom boiler tube. Another cause of NO Baffle is, the cooling unit has been replaced and Dometic Cooling units do not come with new baffles and inexperienced people fail to transfer the baffle from the old to new cooling unit. Doug