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i have a problem on a 110,000 btu/in furnace while checking it i found only 2.4" manifold pressure.adjustng the regulator in the gas valve did nothing.i checked the inlet pressure with the burner off,and found it to be 5.5".as soon as the burner fired it dropped to 2.4".so obviously there is not a problem with the gas valve.i always thought that the min. inlet pressure should be held when the burner fired,and not drop that low. this was the only gas fired appliance firing in the house when this test was being done.the system has csst,running from a manifold in the basement with a main pressre regulator attached to it.i have not adjusted that yet,and did not want to for fear of harming other appliances connected to it.any suggestions before i call the gas company to correct this low gas pressure issue would be appricated.it is about a 30' run from the furnace to the manifold,and it is ran in 1/2 csst piping.thank you