Zero conditional

[Sarapul]

Hello, everybody!
All English grammar coursebooks I have seen state that Zero Conditional refers to something that is always true (and therefore is always CERTAIN) and has a form “Present Simple + Present Simple”. But if I want to say something like that but putting a special focus on the fact that I have in mind some PAST or FUTURE situation or event, can I use a construction “Past Simple + Past Simple” and “Future Simple + Future Simple” correspondingly? For example, I’m talking to somebody about our common friend who doesn’t believe that the lower the atmospheric pressure the lower the temperature when water starts to boil. We know that our friend was in the mountains last week and is going to visit the mountains once again in a week. And we know that he is a kind of obsessed with checking the above-said phenomena and a month ago he declared that he would check it up at first convenience while visiting mountains. Then is it grammatically correct to say:
1. If he heated water when he was in the mountains last time it (CERTAINLY) started to boil at a lower temperature, than at 100 degrees Centigrade. He saw it FOR CERTAIN, because this is law of nature!
2. If he will heat water when he is in the mountains next time it (CERTAINLY) will start to boil at a lower temperature, than at 100 degrees Centigrade. He will see it FOR CERTAIN, because this is law of nature!

Thank you in advance for your reply.
Truly yours,
Alexander

[Alan]

Re. 1: Yes, a past tense variation of this kind on the zero conditional is perfectly feasible. 'If' here essentially means no more than 'whenever'.

Re. 2: Structurally possible, but semantically implausible in the case cited. 'Will' in an if-clause occurs only where the meaning is 'be happy/prepared/willing to', as in

If you WILL kindly sign this check, I'll get it cashed.