Overheating of Solar Geysers

Why is Solar Geysers Overheating?

Let us look at the facts.

Solar Geyser System temperatures can reach dangerously high temperatures - close to or even boiling point (70 to 98°C). If sufficient hot water is not used during hot sunny days, the temperature of the solar water heating system (and geyser) will just keep on rising because no cold water is entering the system to bring the temperature down.


The problem is that most households these days only use hot water in the evening or early morning when people are at home – coming home, going to bed or getting ready for work in the morning.

During hot sunny days when solar heating is most efficient they are at work. No hot water usage is taking place during the day and the solar geyser system temperature just keeps on rising.

With the current drought experienced in the Western Cape and other parts of South Africa overheating of solar geyser systems is even worst. This is caused by using less water in a drive to save water, which in turn means less hot water is consumed.

Another factor that contributes to overheating is over designing of solar collectors. Some experts might reason that to ensure enough hot water is available for a household the collector needs to be overdesigned.

Although this practice cause faster heating of the solar hot water system, it can cause overheating if the hot water is not consumed efficiently to prevent overheating.

The use of EVT (Evacuated Tube) solar collectors can also worsen an overheating situation due to their high efficiency, especially if overdesigned.

How to Prevent Overheating of Solar Water Heating Systems

The most obvious way is to use hot water during hot sunny days – which is not always possible.

Another option is to shade or partly cover the collector.


Options like heat dump systems, heat exchangers and expansion tanks are actually not preventing overheating but compensating for excessive heat and pressure build-up in the solar water heating system.


In many cases controllers are installed which stop the circulation pump when the geyser temperature rises above a certain temperature, claiming to control the temperature.

Overcoming Overheating

This however is not solving the overheating problem. Although the geyser temperature will not increase anymore the temperature in the collector still keeps on rising. Actually by stopping the pump temperature in the collector will increase drastically and much faster.

Helderberg Solar Energy is investigating a control system which will enable us to regulate the solar water heating system temperature of both EVT and Flat Plate collector systems. As soon as the control system has passed all the tests and is proven to be reliable it will be made available to the marketplace.

5 thoughts on “Overheating of Solar Geysers”

  1. Please advise, if you have a solition for overheating solar panels. My geyser overheats, ovetflows 100litres through outlet pipe

    1. Good day Ann, I will be in touch to discuss your problem. It might or might not be overheating. It could also be a faulty safety valve.

  2. I have a 300l and a 150l solar apollo geysers which overheat when i go away for a few days, i would like to know if you have a cover i can put over the tubes that will prevent the overheating

    1. Hi, Spike
      How did you resolve this prblm? I am currently facing similar situation whereby the geyser is overheating during the day.

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