A homeowner bought a high-end Rinnai tankless water heater with built-in recirculation, app controls, and a Bluetooth button — yet their shower still took about two minutes to get warm. The complaint struck a nerve because many buyers expect recirculation to cut both the wait for hot water and cold water wasted down the drain.

Here's what to know

In a Reddit post on r/HomeImprovement, the homeowner described an under-sink recirculation valve and said the result was the same whether recirculation started through the heater's iOS app or Bluetooth button: "It takes at least two minutes for it to be comfortable enough to go in."

The takeaway from the thread was that the bottleneck may be the home's plumbing configuration, not the heater itself. "The premise is that you put the valve on your farthest fixture so it gets hot water fairly close to everything," one commenter said.

So, if the shower was fed by its own branch line and not actually sharing much piping with the nearby shower, hot water may reach the nearby sink sooner without doing much for the shower, weakening the expected benefit of a costly recirculation upgrade.

More background

Users identified the part shown under the sink, shown in a picture the OP shared, as a temperature-controlled crossover valve. One commenter said it allowed the system to move "formerly hot" water through the cold line until hot water showed up.

The user who mentioned "the premise" also suggested a quick way to check whether the setup was functioning: "With the crossover valve, if it's working, you should be getting warm water from the cold side of that fixture shortly after it starts recirculating. If you aren't, then the recirculation itself isn't working."

The same commenter noted that putting the valve under the sink beside the shower is often enough, but only when the fixtures share the same run, writing, "If the shower had its own line run from it (instead of being split off from a single line for the whole bathroom), it won't help much."

Others focused on the utility trade-off. "All you're really trading is water usage for energy usage," one commenter said. In practice, that means less water may go down the drain while the system uses extra energy to keep hot water ready.

What can be done?

The most practical advice in the thread was to start recirculation before shower time and verify that the feature was turned on and working. 

Other suggestions included installing crossover valves in more than one spot or linking recirculation to home automation triggers such as arriving home or bathroom motion. That may improve timing or expand the fixtures that benefit, though it still will not fix a shower with a separate plumbing run.

If this has made you question tankless recirculating water heaters but you're still comparing options, Cala makes smart heat pump water heaters. Its customizable smart heat pump water heaters help homeowners decrease their energy bills by learning to heat water more when it's needed, such as mornings.

While no tank may change how fast the water in it gets to your shower, Cala also has smart features for heating the water when energy is cheapest, which can make it worth a look to offset hot water costs over the long run.

Where can I learn more?

For more on the tankless performance and recirculation issues raised here, these articles examine hot-water delays and what homeowners can realistically expect. 

• Across the U.S., buyers weighing tankless water heater trade-offs often balance efficiency, cost, and convenience.

• Many households find tankless savings claims depend heavily on usage patterns and installation details.

• One homeowner learned tankless showers go weak when other fixtures demand water.

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