Ripple Control: Why Your Hot Water Runs Cold on Winter Mornings

It is the coldest morning of the year. The first shower is lukewarm. The second is freezing. You check the meter box, find nothing obviously wrong, press the boost button — and nothing happens.

Nothing is broken. You have just met ripple control.

What is ripple control?

Ripple control lets your local lines company switch off the power to your hot water cylinder for a while, without touching anything else in your house. Your lights, your heat pump and your oven carry on as normal. Only the cylinders AC power is dead.

It has been part of the New Zealand power system since the 1950s, and most homes with electric hot water are on it. It is not a fault.

Why do they do it?

Everyone turns things on at roughly the same moment: early morning, and again when we all get home. The whole network has to be built to handle those two spikes, and that is expensive.

Cylinders are the perfect thing to switch off during them. A cylinder is basically a big thermos, so turning the element off does not take your hot water away — it just stops you making more for a while. Most days, nobody notices.

Why am I on it?

Because it is cheaper. Look at your power bill: if hot water shows up as its own line, or your plan mentions a "controlled" rate, you are on ripple control. You pay less per unit for water heating, and in return the lines company can pause it during busy periods. For most households, most of the year, that is a good deal.

So why does it bite in winter?

Three things pile up in winter that is unlikely in summer.

The busy periods last longer, because cold weather pushes demand up. The water coming into your cylinder is much colder — around 11 °C instead of 20 °C — so every shower drains more heat out of it. And you are using more hot water anyway.

Put those together and the cylinder runs out at exactly the wrong moment.

Why doesn't the boost button work?

The boost button works by switching on the electric element in your cylinder. If the lines company has cut the power to that element, there is nothing for the boost to switch on. It is not broken — the power simply is not there.

Some systems display a message saying exactly that, such as "AC supply required for boost or legionella setting". Once the network restores the supply, boost works again by itself.

What if my power is back after a storm but the hot water isn't?

In parts of New Zealand, hot water is controlled by separate wires on the network. After a storm the main power lines are fixed first and those wires afterwards, so your cylinder never gets the message to switch back on. Hot water can lag a few days behind the rest of your power.

What can I do about it?

Find out if you are on it. One phone call to your power company will tell you.  You might also have a red light on your metering board, indicating it's active.

Ask to come off it. You can move to an "uncontrolled" plan, which guarantees your hot water is always available. You will pay a bit more per unit, so it is a genuine trade-off rather than an obvious win.

Heat earlier. If your system can be scheduled, set it to warm the cylinder before the morning rush rather than during it.

Check your cylinder size. A small cylinder in a busy household has almost no room for error. A bigger one rides through easily.

Put solar on it. This is the only option that takes the problem away completely.

How solar changes the picture

Ripple control can only switch off power coming from the grid. That is its whole trick — and also its limit.

A Sol•Flare system sends power straight from the panels on your roof into your existing cylinder. That energy never goes through your meter or through the switch the lines company controls. Nobody at a network control room can turn it off.

So on that freezing morning, the cylinders down your street stayed cold until the network let them heat again. The ones with solar started warming at first light and kept going all day.

That is not clever marketing. It is simply a different place for the energy to come from.

Common questions

How long does it last? Anywhere from under an hour to several hours, depending on your area and how cold it is.

Will my water go cold every time? Usually not. A good cylinder holds its heat for hours. Trouble starts when the power goes off while the cylinder is already low.

Does it affect solar hot water? Not a Sol•Flare. Power from your panels goes straight into the cylinder and bypasses the controlled circuit completely.

Tired of cold showers on the coldest mornings?

We will look at your cylinder, your household and your roof, and tell you honestly whether solar hot water will fix it.

0800 20 60 20 | info@oneenergy.nz | oneenergy.nz

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