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Will Turning Water Off Affect My Boiler?


Yes. It will. However, the effect won’t be as bad as operating your kettle without water. Unlike kettles, boilers won’t overheat if there isn’t water in the system. Nonetheless, you should expect other side effects that we’ll talk about later in the article.

Are you interested in learning more about water supply and circulation in boilers and central heating systems? The continue reading.

The three main types of boilers

To understand boiler water circulation, first, you need to appreciate the three main types of boilers. Indeed, they achieve the same result of heating your water and home. Nonetheless, their operations differ slightly.

  • Combination (Combi) boilers.
  • System boilers.
  • Regular (Heat-only) Boilers.

As expected, turning water off will affect each of these boilers differently.

Combination (Combi) boilers

Combi boilers are famous because of their ability to satisfy our need for instant gratification. They produce hot water on demand (Instantly). Therefore, they do not need tanks or cylinders.

In simple terms, they pass your mains water through a heat exchanger circulating boiled water. The boiler water then heats your mains water. It’s important to note that the boiled water in the heat exchanger is independent of your main water supply.

Because of the independence, your combi boiler is less likely to get affected if you turn off the water supply. The only thing that can negatively affect your boiler is if the water in the heat exchanger keeps on heating and significantly raises the structure’s temperature to the point of weakening it. That said, it’s unlikely to happen because most modern Combi boilers have sensors that will automatically shut down the system if the temperatures reach unhealthy levels.

If you still want to use your Combi boiler for, let’s say, room heating, we advise you not to open any taps after turning off the water supply. By not opening them, you’ll not trigger the boiler to heat the water in the exchanger.

System boilers

System boilers significantly differ from Combi boilers. They don’t produce hot water instantly. Additionally, they also make use of hot water cylinders.

First, mains water is directed to a cylinder. Thereafter, the system boiler circulates hot water around it to heat the water within. Once again, it’s important to note that the hot water circulating the cylinder is independent of your mains water supply.

Just like Combi boilers, if there is no cold water to absorb the heat, the water in the exchanger will keep on heating to a certain point. Similarly, they also have sensors that will shut down the unit.

Do you still want to use your system boiler to keep warm? Then don’t open any taps after turning off the water supply.

Regular (Heat-only) boilers

Regular boilers are somewhat similar to System boilers. However, besides the hot water cylinder, they have an additional cold water tank supplying it with cold water. Therefore, unlike Combi and System boilers, its hot water isn’t under pressure from the mains. The hot water pressure comes from gravity. It’s the main reason why the cold water tank is usually on higher ground.

Note: We’ve occasionally emphasized that the water in the heat exchanges is independent of your mains water supply. Specifically, it’s continuous and in a closed-loop within the boiler’s heat exchanger. When you turn on your boiler, it heats up the water in the exchanger, which then heats the water flowing through your pipes. This is true for all three types of boilers.

Leaks – The most common reason for turning off the water supply

If your pipes or system is leaking, you must turn off the water supply to avoid flooding and further unit damage. Below are some of the causes for leaks in boilers:

  • Loose drain valves.
  • Damaged hot water cylinders and cold water tanks.
  • Very high boiler pressure due to high temperatures.
  • Component damage.
  • Leaks are common in old boilers (7 plus years).

How to deal with a boiler leak

Your first move should be to try and locate the leak with observation. Remember, you should never attempt to open the boiler unit. It’s dangerous and scared. You better leave it to certified Gas Safe engineers.

Next, quickly turn off the water supply by closing the heater’s water valve. If you can’t find it or it’s broken, turn off the water at the stop clock. It’s usually located somewhere underneath your kitchen sink.

No. It’s not an actual clock. Instead, it might either be a valve or tap. Because they’re rarely touched, yours might be harder to close. Don’t panic. Find a strong friend or neighbour to help you out.

Can’t find the stop clock?

No worries. You have another alternative. There’s a water supply valve located outside the house. As you might have guessed, this is a more aggressive move. You’ll have to contact your local water authority and have them close it for you because you’ll most probably be sharing it with your neighbours.

Sometimes it might not work…

The solutions we’ve offered above will work if the leak is pipe-related. However, if your tank or cylinder is leaking, they won’t immediately stop the leak. This is because the vessel will first need to empty itself to a level below the leak.

Nonetheless, turning off your mains water supply will prevent the tank or cylinder from refilling.

After turning off the water supply, contact a plumber or heating engineer and have him diagnose your system. In the meantime, you can check your boiler insurance policy.

Other reasons for turning off the water supply

Some people like turning off their water supply when they leave their houses for several days. It’s not a bad idea. They do this, especially during the winter, to prevent bursting as a result of frozen pipes.

On the other hand, we advise you to, instead, leave on the central heating. Not only will it stop the house from getting too cold, but it will also prevent the pipes from getting too cold. Most modern boilers come with “vacation,” “winter,” or “summer” modes.


Yes. Turning off the water supply will affect your boiler. However, most boilers come with sensors that will stop the risk from escalating.

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