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Carlin 301gas in Weil Mclain 480
I just replaced 2 Carlin 201CRD burners in Weil Mclain 480's with Carlin 301GAS. The boilers were thoroughly cleaned and new refractories installed at burner replacement. All the numbers are within Carlin specs but I have a pronounced shudder upon ignition. It goes away after a few seconds and both units are fine for the entire cycle. I talked with Carlin tech support and couldn't come up with an answer. Any ideas? Thanks