There are two hot-water annoyances almost everyone in Medellín knows. The first is opening the faucet at the farthest sink and waiting a long minute, cold water running down the drain, until lukewarm finally arrives. The second is the shower that goes hot, cold, hot, cold — right when you have shampoo in your hair.

Both have concrete causes and simple fixes. Neither requires replacing the water heater or remodeling the bathroom. And both improve a lot when the house runs them on its own.

Why hot water takes so long to arrive

The heater sits somewhere in the home — usually the laundry area, the kitchen, or a balcony. Between the heater and the primary bedroom sink there can be fifteen or twenty meters of pipe. When nobody has used hot water for a while, that whole run is full of water that has already cooled.

When you open the faucet, all that cold water has to come out before hot water arrives. That's the wait — and why liters of water are wasted every time.

The recirculator at the farthest sink

A recirculator is a small pump that moves water through the hot line so cold water returns to the heater and hot water sits waiting near the faucet. The most practical version for an existing home installs under the sink farthest from the heater and uses the cold-water pipe as the return — so you don't need to open walls for a new return line.

When the pump runs, it pushes water from the hot line into the cold through a valve under the sink. That water returns to the heater via the cold network. In a couple of minutes, the hot line is full of hot water all the way to the last fixture. Every sink and shower along the way benefits too.

One important detail: this setup works best with tank heaters. With tankless (on-demand) heaters you have to check whether the unit supports recirculation — some need a minimum flow to ignite that a small pump can't reach. That gets decided before you buy anything.

A simple pump, controlled by the house

There are recirculators with their own timers and sensors, but we prefer the opposite: a plain pump with no smart features, plugged into a Zigbee smart outlet. The pump only knows on and off. The house provides the intelligence.

That has several advantages. The pump is easier to source and replace. Control lives in the same app that runs the rest of the home. And the Zigbee outlet, always powered, acts as a repeater and strengthens the mesh network — as we explain in the Zigbee and Thread guide.

With that, the pump can turn on in several ways:

1. By schedule. Ten minutes before the house wakes up, and another cycle late in the afternoon.
2. By presence. When a sensor detects someone entering the main bathroom, the pump runs for a couple of minutes.
3. On demand. A button by the sink or a command from the app.
4. With a time limit. It always shuts itself off after a few minutes, so you don't waste energy heating water nobody will use.

Leaving the pump on all day wastes energy and forces the heater to replace heat lost in the pipes. Running it only when needed gives the same result with far less consumption.

Why the shower goes from hot to cold

This problem is very common in Medellín, especially in houses and apartments with gas tankless heaters. To understand it, you need to know how that heater works.

A tankless heater doesn't store hot water. It heats water as it passes through. To know when to light the burner, it has a flow sensor: if enough water is flowing, it ignites; if flow drops below a minimum, it shuts off the flame.

That's the problem. When water pressure in the home isn't steady, flow rises and falls. Someone opens the kitchen faucet, a toilet refills, the building tank changes level, or municipal pressure varies by hour. In the shower, that feels like a drop in flow. If flow drops enough, the heater kills the flame. A moment later pressure recovers, flow rises again, and the heater relights. The result is the hot-cold-hot-cold shower.

Something less obvious happens too. Even if the heater doesn't shut off, with less water passing through it the temperature rises, and with more water it falls. Unstable pressure makes the temperature change even when nobody touches the valve.

The booster pump

The fix is to keep pressure steady. That's what a booster (pressurizer) pump does — installed at the home's water inlet or on the line feeding the heater and bathrooms. The pump senses pressure and holds it stable even when the municipal supply or tank varies. With stable pressure, shower flow is stable too, the heater stays lit, and temperature stays where you set it.

Some booster pumps have electronic pressure control that varies motor speed with demand; simpler ones turn on and off with a pressure switch. The first kind are quieter and give more even pressure — something you notice a lot in the shower. The choice depends on home size, number of bathrooms, and incoming pressure.

Automate it so it only runs with the shower

A booster pump doesn't need to be on all day. For the shower problem, it's enough that it runs while someone is bathing. The house can handle that:

• By bathroom presence. When someone enters, the pump is ready. When the bathroom has been empty for a few minutes, it turns off.
• By shower flow. A sensor on the drain or shower line detects water running, turns the pump on, and turns it off when flow stops.
• By schedule, as a backup during the hours the household usually showers.

That cuts noise, electricity use, and motor wear — and the shower holds temperature.

The technical side, without shortcuts

Here you have to be careful, because you're dealing with motors and pressurized pipe.

1. The outlet or relay must be sized for the motor load. A motor draws much more at startup than once it's spinning. A common smart outlet can work for a small recirculation pump, but a booster pump needs a relay or contactor rated for motor loads — not just the pump's nominal wattage.
2. Electrical work is done by an electrician. The booster pump usually gets its own circuit and protection. If the control goes inside a panel or a recessed box, a licensed electrician installs that too.
3. Plumbing is done by a plumber. Mounting a booster or recirculator means cutting pipe, adding check valves, and leaving everything sealed and tested.
4. The pump must be able to run in manual mode. If the home system fails, there has to be a way to turn it on directly.

We design the system, choose the equipment, and integrate it into your app. Electrical and plumbing installs are done by pros experienced in each trade.

How it looks in the app

Everything lives in your own app, built for your home. You can see whether the recirculator ran this morning, change the schedule, turn the booster on by hand, or check how long each pump ran each day. If the outlet or relay measures consumption, you also see how much energy each pump uses. No subscription.

The result is simple: hot water as soon as you open the faucet anywhere in the house, and a shower that stays at the same temperature from start to finish.