The Large Commercial Technical support team has received a number of calls on the Gas Heat Primary Limit Open diagnostic (E02 for the 1285 and a flash code of RED 51 for the 1287 staged). If the Gas heat is a 600 MBH burner then there are 5 devices that are wired in series with the "High Limit" input (3 Gas Pressure switches, a Flame Rollout, and a High Temp limit). The Pressure switches should all be set to ~5" iwc...the Supply/low gas pressure switch should open if the Supply Gas Pressure falls below 5" and the 2 manifold/high gas pressure switches should open if the manifold/leaving gas pressure from the switches rises above 5". The input is a 24Vac input and so you can verify that the module output is 24 Vac and the input is receiving 24Vac. For testing purposes ONLY you can temporarily add a jumper between the Orange wires (J7 pins 2 & 15 on the 1285 modulating board and J4 pins 9&10 on the 1287 Staged board). Attached are the schematics for the IGN1 modules for modulating and staged heat burners.
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.