How To Adjust Boiler Water Temperature

There are three types of Boilers in UK homes up and down the country, Combination Boilers, System Boilers, and Heat-only Boilers. 

Whatever type of Boiler you have, it’s crucial to maintain the correct water temperature in your Boiler for safety and comfort. 

Why Adjust Boiler Water Temperature?

There are several reasons you may want to adjust your Boiler water temperature:

Energy Efficiency 

A Boiler operating at too high a temperature can waste energy and unnecessarily high heating bills. 

Lowering the Boiler water temperature can improve energy efficiency based on the principle of condensing technology in modern Boilers and the general relationship between temperature and energy usage. Here’s how:

Condensing Technology 

High-efficiency condensing Boilers extract heat from the flue gases that would otherwise escape from the Boiler and cool these gases until they ‘condense’, turning into liquid form. Condensing these gases releases extra heat that’s recycled to heat your home. The cooler your Boiler’s water temperature, the more these gases will condense, and the more heat can be recovered, thus improving energy efficiency.

Lower Energy Usage

The higher the temperature at which your Boiler operates, the more energy it requires to reach and maintain that temperature. Reducing the set temperature requires less energy to heat the water to that level, resulting in less energy consumption.

Reduced Heat Loss

Lowering the Boiler water temperature minimises heat loss from the Boiler and pipework. The greater the difference between the temperature inside and outside the pipes, the more heat is lost. By reducing the temperature of the water, this difference is reduced, and less heat is lost.

Enhanced Comfort 

Lower water temperatures can lead to more consistent and comfortable indoor temperatures. This can reduce the likelihood of overheating and subsequent unnecessary Boiler cycling, improving overall energy efficiency.

Comfort Levels

If your home isn’t warm enough or too warm, you might need to adjust the Boiler water temperature. A slight increase or decrease can make a significant difference in comfort levels.

Adjusting the Boiler water temperature can directly impact the heat levels of your radiators. Here’s how:

• Increasing Boiler Water Temperature: If you increase your Boiler’s water temperature, the water circulating through the radiators will be hotter. This means the radiators will emit more heat, making the room warmer. However, it’s important not to raise the temperature excessively, as it can lead to energy wastage and a potential scalding hazard.
• Decreasing Boiler Water Temperature: If you lower the Boiler’s water temperature, the water flowing into the radiators will be cooler. This results in less heat being radiated, potentially making the room cooler. Lowering the temperature might be useful during warmer months when less heating is needed or if you’re trying to conserve energy.

The balance is to find a Boiler water temperature that provides sufficient heat to maintain comfort levels while optimising energy efficiency. Remember that different rooms might require different temperatures, so using thermostatic radiator valves better control individual room temperatures.

Also, remember that the heat output from your radiators isn’t only dependent on the Boiler water temperature. The size and type of radiators, insulation levels in your home, and the outside temperature all affect how effectively your heating system can warm your home.

System Longevity

Running a Boiler at excessively high temperatures can lead to several issues that place unnecessary stress on the Boiler and the central heating system, potentially leading to decreased efficiency, increased energy costs, and a reduced lifespan for the system. Here’s how:

• Overheating Components: High temperatures can cause Boiler components to overheat and potentially fail. This can result in expensive repairs and even Boiler replacement if the damage is severe.
• Expansion and Contraction: A Boiler’s heating and cooling cycles cause its components to expand and contract. When the Boiler runs at higher temperatures, this expansion and contraction are more extreme, leading to wear and tear over time, potentially causing leaks or system breakdowns.
• Increased Pressure: Higher temperatures can lead to increased pressure in the system. If this pressure becomes too high, it can strain the Boiler and associated pipework, leading to potential leaks or other damage.
• Efficiency Loss: While it may seem counterintuitive, running a Boiler at high temperatures can reduce efficiency. This is particularly true for condensing Boilers, which work most efficiently when the return water temperature is low enough for the flue gases to condense.
• Short Cycling: Boilers that run at very high temperatures can lead to a problem called short cycling, where the Boiler frequently turns on and off in short periods. This wastes energy and puts extra wear and tear on the Boiler’s components, reducing the system’s lifespan.

To avoid these issues, it’s crucial to maintain your Boiler at the recommended temperature settings, ensuring it’s not running too hot. Regular servicing by a professional can also help to identify and rectify potential issues before they become major problems.

Safety Concerns

Boiler water temperature can pose a scalding risk when it’s too high. Here’s why:

Boilers heat the water circulated to various outlets in your home, such as taps, showers, and radiators. If the water temperature in the Boiler is set too high, the water coming out of your taps and showers can also be extremely hot.

When water at such high temperatures comes into contact with the skin, it can cause scalding injuries. This risk is particularly high for vulnerable individuals, such as children and the elderly, who have more sensitive skin and may not react as quickly to hot water.

According to the Burn Foundation, hot water can cause third-degree burns in adults in just five seconds at 60 degrees Celsius and in just one second at 70 degrees Celsius.

Therefore, setting your Boiler’s water temperature to a safe level is crucial. 

However, remember that the optimal setting can vary based on specific circumstances, so consult your Boiler’s manual or a heating professional if you’re unsure. 

Also, consider installing thermostatic mixing valves (TMVs) on taps and showers, as these devices help to regulate the water temperature and prevent scalding.

Preventing Legionella

Legionella is a type of bacteria that can grow in water systems, causing Legionnaires’ disease, a severe form of pneumonia, when inhaled through aerosols or aspirated (see below for more information)

To prevent the growth of these bacteria, the water temperature in your Boiler should be set at a minimum of 60 degrees Celsius. Legionella bacteria are killed at 60 °C+

Never set your Boiler below 60 °C

Remember, while adjusting your Boiler’s water temperature can have several benefits, it’s important to ensure that any adjustments align with the manufacturer’s recommendations and safety guidelines.

Adjusting Boiler Water Temperature

Here’s how to adjust Boiler water temperature for Combination, System and Regular Boilers.

Adjusting Water Temperature for Combination Boilers

Combination Boilers, or “Combi” Boilers, are efficient units that provide hot water and central heating. They heat water directly from the mains supply when you need it, eliminating the need for a storage cylinder. 

Find the temperature control dial or digital display on the front panel to adjust the water temperature on a Combi Boiler. 

Turn it to your preferred setting for hot water, usually between 60-65 degrees Celsius. 

Adjusting Water Temperature for System Boilers

Unlike Combi Boilers, System Boilers use a cylinder to store hot water. 

To adjust the temperature on a System Boiler, locate the cylinder thermostat, often found on the hot water cylinder itself. 

Adjust the dial to your desired temperature, which should be around 60-65 degrees Celsius for most homes. 

This temperature ensures hot water without the risk of scalding and reduces the chances of bacteria growth.

Adjusting Water Temperature for Heat Only Boilers

Heat-only Boilers, also known as regular, traditional, or conventional Boilers, include a hot water cylinder and a cold-water storage tank. 

Typically, the Boiler thermostat controls the temperature of the water heated by the Boiler, while a separate cylinder thermostat controls the water stored in the cylinder. 

Like system Boilers, adjust these thermostats to your desired temperature, ideally around 60 degrees Celsius for the cylinder.