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A heat pump hot water system against the side wall of a single-storey house at dusk, beside a potted plant and a lit living room.

Run the hot water on off-peak or solar

How it works

An Ogemray 25A goes in the hot water system's supply and switches it. One schedule, stored on the relay, turns the circuit on when your cheap window starts and off again after the hours you set. Inside that window the tank's own thermostat does what it always has, heating until the water is hot and then stopping.

The relay also measures power, so the app shows the element drawing while it heats and charts the energy each day. Change your plan, or add solar, and you change one time in the app.

  1. Shelly app Schedule screen for an Ogemray 25A named Hot water, with two daily schedules: On at 00:00 for 21600 seconds and On at 11:00 for 10800 seconds. 01

    Your phone

    Set the heating window from the app and see what each heat-up uses.

  2. Ogemray 25A Smart Relay 02

    Shelly relay

    Lets the element heat only in your cheap window, then switches it off.

  3. 03

    Your hot water system

    Heats on cheap power. Its thermostat still decides how hot.

Check your hot water and your plan first

This is for an electric hot water system. Look at your bill: if the hot water is on a controlled-load tariff, it already heats off-peak. Otherwise, find your plan's off-peak window, and check the element's rating on the tank's rating plate (up to 6000 W for the Ogemray 25A).

What it looks like on your phone

  • Two cheap windows. Midnight for six hours, and 11 am for three, every day.

  • The start time. Set it to when your cheap rate begins.

  • The run time. On, then back off after the seconds you choose.

Step by step

How you'll set it up

Add the device to Wi-Fi from your phone, or straight from a browser.

Download Shelly Smart Control on the App Store Get Shelly Smart Control on Google Play

  1. Fit the relay to the hot water circuit

    Mains goes to L and N. L1 feeds the hot water system, and its neutral runs back as before. S1 and COM stay empty.

    Wire map Ogemray 25A
    • Active (supply) L
    • Neutral N
    • Hot water system L1
    Circuit overview
    LN230 V~ 50 HzHot water systemL1LNCOMS1Ogemray 25A
    Active (supply)Neutral / 0 VSwitched load

    In Australia, fixed 230 V wiring is licensed-electrician work. Use these diagrams to plan the job and brief your electrician.

    Showing the whole circuit

    Ogemray 25A

    100%
    LN230 V~ 50 HzHot water systemL1LNCOMS1Ogemray 25A

    Select a terminal to follow its wiring.

  2. Add it to the Shelly app and name it Hot water

    Add the relay in the Shelly Smart Control app and name it Hot water, so the schedule and the power readings say what they're for.

    Learn how to add a device to the Shelly app

  3. Add a daily schedule

    Open Schedule and tap Add schedule. With Simple selected, tick every day under Choose Weekday and tap Next. Leave Choose time interval on Time, set the start of your cheapest overnight window (00:00 here) and tap Next. In the web interface, open Schedules and click Create schedule, enter the Time and select every day.

  4. Heat for six hours, then stop

    Tap Add local action and choose Control Output. Set it to On, turn on Toggle value after and enter 21600, which is six hours in seconds. Tap Save, then Next, then Save. In the web interface, click Add action to execute, choose Control Output, set it to On and Flip value after to 21600, then click Save local action and Save.

  5. Add a midday window, if your plan has one

    Some plans add a cheaper window in the middle of the day, when solar floods the grid. Add a second schedule the same way: every day at 11:00, On, with Toggle value after set to 10800, which is three hours. The tank then heats from midnight to 6 am and again from 11 am to 2 pm.

  6. Check the schedule

    Schedule now lists the overnight window: On at 00:00, toggling back after 21600 seconds, every day. If you added the midday window, it's on the line below. Schedules in the web interface shows the same list.

  7. Adjust it to suit your household

    Give it a week or two. If the hot water starts running out during evening showers, add a second schedule for a top-up: every day at 18:00, On, with Toggle value after set to 3600, which is one hour. That hour is usually at the dearer rate, so keep it short. If the energy chart shows the element stopping well before the overnight window ends, shorten that one instead.

Frequently asked questions

My hot water is already on off-peak. Do I need this?

If your bill shows a controlled-load tariff for the hot water, your network already switches it to off-peak hours, and a relay adds a power reading but no saving. This page is for a hot water system on your main tariff, such as a time-of-use plan, or one you want to run on solar instead.

How do I run it on my solar instead?

Set the schedule to start late morning, say 10:00, while the panels are producing, and run it for five hours (18000 seconds). On a cloudy week the tank may not get hot enough, so add a short overnight schedule as a top-up.

Will I run out of hot water?

Not if the window is long enough for the tank to reheat after a day's use. The energy chart shows when the element stops drawing each day; if it's still drawing when the schedule ends, lengthen the window.

Does it work with a heat pump?

A heat pump draws much less than an element, and many have their own timer. Check its manual first: if it has a timer, use that; if it's happy to have its power switched, the relay works the same way.

What size hot water system will the relay handle?

Up to 25 A, or 6000 W. The element rating is on the tank's rating plate; a typical electric storage tank is well inside that.

What happens if the internet drops out?

The schedule is stored on the relay, so it keeps running on its own. The relay sets its clock over the internet, though, so a long outage or a reset can leave the times out until it reconnects.

Can I turn the hot water on outside the schedule?

Yes. Tap the relay in the app to turn it on, for a top-up after guests, say. The schedule turns it off again at the end of its window, or set an auto-off so it doesn't run longer than you meant.

Can it follow live prices instead?

Yes, if your retailer offers them to Home Assistant. Amber Electric has a built-in integration with a live price sensor: point the automation at that sensor instead of your own, and the hot water heats whenever power is cheap. Some other retailers have community integrations.

Should I also set a schedule in the Shelly app?

No. Let Home Assistant do the switching. A schedule on the relay as well would turn the hot water on and off at its own times, fighting the automation.

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