What I was thinking, was using an AC in my office and using the waste heat to heat up the water in my boiler

The HVAC technician I talked about that laughed at me and said, that's science fiction

But I don't really get why.
Wouldn't that be just a heat pump from the perspective of the boiler and an AC for my office?

Edit: to clarify, I'm aware, that I can't heat up the water to the level I want with that, but I could pre-heat it, so I don't need so much power to heat it the rest of the way

Edit 2: and I guess, there is my answer
My boiler usually doesn't get that low on heat, that this would really make an impact, as it usually hotter than the waste heat

Still, I think, there should be a way to gather the waste heat somehow