It’s expanding, don’t stop it, you can’t.
it is a safety feature on most instantaneous water heaters, if it did’nt expand, it would rupture with devastating results.

Whoever did the plumbing on your new construction should be contacted–[or the general contractor or builder] before you “sign off” and move in. There should be a brochure or manual or warranty document for that instant hot water gadget of yours [look in a kitchen drawer or ask the builder] with trouble-shooting or FAQ’s related to the product. NOW is the time to get things replaced — easier now than later, you still have leverage.