Should I shut off the main myself?
If you can’t isolate it at the fixture, yes — use the main, but only if you can reach and operate it safely.
Why does this drain keep coming back?
Repeat clogging usually points past the trap — check the branch, the vent, and the slope before assuming it’s simple.
Tank or tankless — how do I decide?
It comes down to how much hot water the house pulls at once, what’s already piped for fuel and venting, and what the panel can spare.
Does older pipe always mean full replacement?
Not always — material, pressure, leak history, and how hard the section is to reach all factor into a patch versus a full repipe.
Who’s checking the provider’s license?
That’s on the homeowner — confirm credentials, insurance, permits, and warranty terms before work starts.