Well, first things first, somehow "Feuerungsaggregaten" and "pilot light(s)" are not the same term, but that statement has its limitations given limited technical expertise with many aspects of fire protection and / or retarding flame propagation / preventing spread of fire.
It sounds like we are taking about a real buidling "firewall" versus the computer peripheral used to protect (networked) computers from (Internet) hackers. Created a link for Firewall Construction in the Quellen / Resources box that may help with your question.
Regarding your real question, there are many possibilities:
Nachweis = proof, demonstration, evidence, maybe qualification test results, certification of equivalence, etc.
Your clause (sentence) can read:
"....without (requiring) proof (etc,) of equivalence..." or,
"...where there is no proof (etc,) of equivalence..."
"...when / if there is no proof (etc,) of equivalence..."
Some of these suggestions would change your translation if it is actually a firewall construction that is discussed versus "pilot light."
For example, firewall already has the word, so you could eliminate "wall(s)" in your translation. It would certainly would change the sentence structure / grammar.
"Custom-built firewalls must have a minimum thickness of 0,12m, when / if / where there is no proof of equivalence (without requiring / demonstrating proof of equivalence).
Hoping that makes sense. :)