I recently replaced a standard hot water heater with a tankless system. I get hot water immediately off a sink 4 feet away. It takes about 45 seconds for my master bedroom shower (20-30 feet away). The laundry which is closer than the shower takes 3-4 minutes. The guest shower which is 70 feet away takes a full 5 minutes. I ran a tee off the line about 4 feet from the heater, directly to the laundry room and now it heats in about 30-45 seconds. I can't figure out what is going on. The volume of water in the pipe to the guest bathroom can't take 5 minutes to clear. The original system was set up with a circulating pump that kept hot water flowing through the pipes at all times (not very energy efficient, but saved water). I'm wondering if that has something to do with the issue, perhaps some kind of large loop? I can't trace pipes as there is no schematic and they are embedded in the concrete slab (no basements in the SW). Thoughts anyone?