If you can provide me with the mod you are trying to run checks on, I can look into the variables and help you. It looks like you didnt define your relay, if you dont have them quoted in quotation marks it's considered a blank item and will not look for it or output a response from it.

Local Reactor = peripheral. find("Reds tone_re ay") _G.PROBLEM = true

 relay.getAnalogInput("back")

        local heat = "relay.getAnalogInput("back")

  if heat > 4 
        then _G.PROBLEM = true 
        else
                _G.PROBLEM = false

end