I have two empire wall heaters.One works fine the other the pilot won't stay lit.I have switched the thermopile or flame reader on them to see if that's the problem and its still the same the one that worked still works with the thermopile from the other and the one that didn't work still doesn't with the other thermopile from the one that dose.Could it be the valve.
Thanks

It could be a dirty or short pilot on the defective unit. It could also be the gas valve. See below link