In the quest to reduce energy bills, one of the most effective yet often overlooked adjustments you can make is to the ‘flow temperature’ on your combi boiler. This simple, free change can significantly increase your boiler’s efficiency and lead to substantial savings on your heating costs. Here’s a comprehensive guide to understanding and mastering this crucial setting.
What is the Boiler Flow Temperature?
The flow temperature is the temperature to which your boiler heats the water before it is sent to your radiators. This is distinct from your main room thermostat, which dictates the desired air temperature for your home, and the hot water temperature for your taps. On a combi boiler, you will typically find separate controls for the radiator heating and the domestic hot water.
Most boilers are installed with the flow temperature set unnecessarily high, often between 75°C and 80°C. While this heats your home quickly, it prevents modern condensing combi boilers from operating in their most efficient mode.
Why Lowering the Flow Temperature Saves Money
Modern condensing boilers are designed to be most efficient when the water returning to the boiler (the ‘return temperature’) is cool enough to trigger the condensation process. This process recovers latent heat from the flue gases that would otherwise be wasted.
When the flow temperature is set too high, the return temperature is also high, and the boiler rarely gets to condense, thus operating inefficiently. By lowering the flow temperature, you ensure the boiler can run in its ‘condensing mode’ more often, using less gas to achieve the same level of comfort in your home.
The Financial and Environmental Benefits
The advantages of adjusting your flow temperature are well-documented and significant:
- Reduced Gas Bills: According to research by organisations like Nesta and the Energy Saving Trust, lowering your flow temperature from 80°C to 60°C can reduce your gas usage for heating by approximately 9% to 12%. For the average household, this could equate to a saving of over £100 per year.
- Increased Boiler Lifespan: Operating at a lower temperature reduces the thermal stress on the internal components of your boiler, which can lead to fewer breakdowns and a longer operational life.
- Lower Carbon Footprint: By using less gas, you are also reducing your home’s carbon emissions, contributing to a greener environment.
Recommended Flow Temperature Settings
For most modern condensing combi boilers in the UK, the optimal flow temperature is between 55°C and 65°C.
- 60°C to 65°C: A great starting point for the colder winter months. This should provide ample heat for most homes.
- 55°C: Ideal for milder autumn and spring weather, or for very well-insulated homes. This temperature will maximise your boiler’s efficiency.
It’s important to note that if you or someone in your household is particularly vulnerable to the cold, it is advisable not to set the flow temperature below 60°C to ensure your home can heat up in a reasonable time.
How to Adjust Your Combi Boiler’s Flow Temperature: A Step-by-Step Guide
Adjusting the flow temperature is a straightforward process that you can do yourself. While the exact controls vary by boiler model, the general steps are as follows:
- Identify the Correct Control: Look at the front of your combi boiler. You should see two separate controls: one for hot water (often indicated by a tap icon) and one for central heating (usually indicated by a radiator icon). You want to adjust the one with the radiator icon.
- Make the Adjustment: This may be a physical dial that you turn or a digital display with buttons to increase or decrease the temperature.
- Set the New Temperature: Turn the dial or use the buttons to lower the radiator flow temperature to your desired setting, for example, 60°C.
- Monitor and Tweak: Over the next few days, observe how your heating performs. If your home feels comfortably warm, you’ve found a good setting. If it feels a little cool, you can increase it slightly. The key is to find the lowest temperature that still keeps your home comfortable.
Important Note: This advice is specifically for combi boilers. If you have a conventional or system boiler with a separate hot water cylinder, you should not lower the boiler’s main thermostat below 65°C. This is to prevent the growth of harmful Legionella bacteria in the stored water.
Potential Drawbacks to Consider
The main trade-off for increased efficiency is that your home may take slightly longer to reach the desired temperature set on your room thermostat. However, for most households, this difference is minimal and far outweighed by the significant cost savings. The radiators themselves may also not feel as scorching hot to the touch, which is perfectly normal.
By taking a few minutes to understand and adjust your combi boiler’s flow temperature, you can take a significant step towards a more energy-efficient home and lower heating bills this winter.
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