How to Change Your Hot Water Heating Times

If you’re wondering how to change hot water heating times, the short version is: work out what type of system and tariff you’re on, then choose the right control — built‑in scheduling for heat pumps, a timer/contactor for electric storage, or leave it as‑is for instantaneous units. Some tariffs (controlled load/off‑peak) are set by the distributor and can’t be user‑changed, but you can often move the heater to a timer on general supply or adjust the system’s own schedule.

What you can (and can’t) change

Before grabbing a screwdriver, check these basics:

• Electric storage on controlled load (off‑peak) — the network controls when it gets power, usually overnight. You can’t change those hours yourself. Your options are request a tariff change via your retailer or have a licensed electrician move the heater to general supply with a timer.
• Electric storage on general supply — you can add a timer and contactor to choose your own heating windows.
• Heat pump hot water — most models have a built‑in controller to set operating times, quiet mode, and a weekly 60 °C boost. You can usually adjust these yourself.
• Gas storage or instantaneous (gas or electric) — instantaneous systems heat on demand, so there’s nothing to “schedule”. Gas storage typically runs via a thermostat, not a timer.
• Solar thermal (roof collectors with a booster) — you can schedule the electric booster with a timer so it tops up at set times.

Step 1: Identify your system and tariff

Take a photo of the unit’s data plate and the switchboard. Check for:

• System type: electric storage cylinder, heat pump, gas storage, or instantaneous.
• Element size (kW): common electric storage elements are 3.6–4.8 kW; heat pumps quote input in kW and COP separately.
• Metering/tariff: look for a “controlled load”, “off‑peak”, “Tariff 31/33”, or similar on your bill or meter. If you have a dedicated off‑peak breaker in the switchboard labelled “HWS/CL”, your hot water is likely network‑controlled.

If you’re unsure, ask your electricity retailer which tariff your hot water is on and whether it’s wired to a controlled load circuit. This dictates how much control you have.

Step 2: Choose how you’ll control heating times

Option A: Use your heat pump’s built‑in scheduler

Most heat pump units have a control panel where you can set one or more time windows (e.g. 10 am–3 pm), a quiet mode for night, and a weekly high‑temperature boost (60 °C) for hygiene. Open the front panel or indoor controller and look for “Timer/Schedule”, “Boost”, and “Temp”. If you have rooftop solar, set the main window to the middle of the day. Ensure the weekly or daily boost to 60 °C is enabled to meet Australian hygiene requirements.

Option B: Add a timer and contactor to an electric storage system

For hard‑wired storage cylinders on general supply, a licensed electrician can fit a switchboard timer and a contactor rated for the element’s load. The timer controls the contactor coil; the contactor switches the high current to the element. You pick the heating windows (e.g. overnight for off‑peak energy plans, or midday for solar self‑consumption).

Important details your sparkie will consider:

• Load rating and inrush current of the contactor relative to the element (e.g. 20–25 A typical for 3.6–4.8 kW).
• Battery/supercap backup in the timer so it keeps time during outages.
• Manual override so you can heat outside the schedule if needed.
• Labelling, RCD/MCB protection, and enclosure IP rating if mounted near moisture.

If your cylinder is currently on controlled load and you want user control, ask your retailer about moving it to general supply, then have a timer/contactor installed. Note this may change your energy costs — check your plan.

Option C: Smart control synced to rooftop solar

If you have solar PV, running a storage heater or heat pump in the late morning to mid‑afternoon usually maximises self‑consumption. You can:

• Set a fixed daytime window (e.g. 10 am–3 pm) with a timer.
• Use a home energy management system that switches the heater on when solar export exceeds a threshold. This still needs a contactor for hard‑wired loads.

Fixed windows are simple and work well for most homes. Smart diverters can shave imports further but add complexity.

Option D: Solar thermal booster scheduling

With roof collectors and an electric booster element, add a timer so the booster only runs late afternoon or evening if the sun hasn’t done the job. Keep the weekly 60 °C sanitising cycle intact.

What you generally can’t change

Instantaneous systems (gas or electric) don’t store water, so there’s nothing to pre‑heat or schedule. You can, however, insulate pipes and reduce shower flow rates to cut gas or electricity use.

Step 3: Set sensible heating windows and temperatures

How many hours do you need? Roughly, a 3.6 kW element can reheat about 250 L from cold in 3–4 hours. In day‑to‑day use you’re only replacing the hot water you used, so 1–3 hours per day often covers a typical family.

• If you chase off‑peak rates: set the timer overnight. If you have a smart meter plan with cheaper shoulder periods, you could add an early‑morning top‑up.
• If you have solar: aim the main window at solar hours. Add a small evening or early‑morning fallback window in winter if showers run cool.
• Temperature: storage and boosters must reach 60 °C in the tank for Legionella control. A thermostatic mixing valve should temper it to ~50 °C at the bathroom taps to prevent scalds. Don’t dial the tank below 60 °C.

Heat pumps: use the built‑in schedule and consider a “quiet” night mode if the unit sits near bedrooms. Many heat pumps recover more slowly in cold weather; widen the window accordingly.

Safety, compliance and good practice

• Electrical work: Anything involving 240 V wiring, switchboards, contactors or timers must be done by a licensed electrician in Australia. Don’t DIY hard‑wired controls.
• Legionella control: ensure the system hits 60 °C in the tank at least weekly (many heat pumps automate this). If you aren’t sure, ask your installer to confirm the sanitising cycle is enabled.
• Scald protection: a thermostatic mixing valve at the outlet mixes down to safe tap temperatures; don’t compensate by lowering the cylinder below 60 °C.
• Insulation: fit a cylinder jacket (if suitable) and insulate the first 1–2 metres of hot and cold pipework for better heat retention.
• Labelling: have the timer schedule and manual override clearly labelled at the switchboard so guests or future owners know how it operates.

Troubleshooting when the timer’s on but water is cold

1. Wrong circuit: The heater may still be on a controlled load circuit. If so, your daytime timer on general supply won’t feed the element. Confirm wiring and have a sparkie move it properly.
2. AM/PM or daylight saving error: Double‑check the timer clock, AM/PM, and daylight saving setting. Many timers default to 24‑hour time.
3. Insufficient run time: Increase the window by 30–60 minutes, especially after heavy use or in winter.
4. Thermostat set too low or faulty: Storage heaters need 60 °C in the tank. If the stat is faulty, the heater may cut out early. Call a plumber or electrician to test and replace.
5. Heat pump low‑ambient limits: In cold, damp conditions some heat pumps reduce output or defrost often. Allow a longer window or enable the electric boost if available.
6. Element failure: If the booster or main element is blown, the timer will switch power but no heating occurs. A licensed tech can test resistance and replace the element.

Will changing heating times actually save money?

Often, yes — but it depends on your plan and usage. Moving an electric storage or heat pump system to align with solar generation can significantly cut grid imports. Shifting to overnight windows can take advantage of lower off‑peak or controlled‑load rates. On single‑rate plans, savings come mostly from using more solar or reducing standby losses by avoiding unnecessary reheats.

As a rule of thumb, pick one main daily window that reliably recovers the tank, then add a short backup window only if you’re occasionally running out. Keep an eye on bill changes after any tariff move. For a deeper dive into pricing, see our guide to off‑peak hot water.

Bottom line: to change hot water heating times, match the control method to your system and tariff, set a sensible schedule that reaches 60 °C regularly, and get a licensed electrician to install any hard‑wired timers. A few tweaks can make your hot water cheaper and more reliable.