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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: February 13, 2024. Updated: February 16, 2024

What Temperature Should My Boiler Be Set At For Hot Water in the UK

Understanding the optimal settings for your central heating system can be complicated. There are many controls such as room thermostats, radiator valves, and boiler thermostats. This guide demystifies these settings, focusing on achieving efficiency without sacrificing comfort.

Optimal Boiler Temperature Settings

Programmable thermostat - what temperature should my boiler be set at for hot water UK | BoilerhutFor combi boilers, the ideal temperature for radiator output is 75°C, and for hot water, it should be between 50°C and 60°C.

Adjusting these preset temperatures may negatively impact the boiler’s efficiency. Viessmann boilers, for example, benefit from weather compensation technology. This can automatically adjust the boiler temperature in response to external conditions. This optimises efficiency.

Setting the temperature too high may heat your home faster but at the cost of increased heating bills. It can also reduce boiler efficiency by approximately 10 to 20%. The recommended maximum radiator temperature is 80°C.

Water Cylinder Thermostat Settings

Homes with conventional boiler systems should adjust their water cylinder thermostat to between 60°C and 65°C . Setting it to 60°C is optimal, but it should not be lower to prevent Legionnaires’ disease. This is a type of pneumonia caused by the Legionella bacteria thriving in temperatures below 60°C. Hot tap water should be lower than the radiator output to ensure efficiency.

Utilising Heating Controls Effectively

Your heating system’s efficiency can be maximised by careful use of all controls. A room thermostat should be set between 18°C and 21°C for your comfort. Bedrooms may be cooler, around 16°C to 18°C, for better sleep. Programmable thermostats offer the flexibility to set different temperatures throughout the day.

Thermostatic Radiator Valves (TRVs) offer additional control. They adjust the water flow through radiators, with a setting of 3 or 4 recommended for a comfortable 20°C room temperature.

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Avoiding Overheating

Resist the urge to turn up the heat at the first sign of cold. Overriding the TRVs or thermostat settings can lead to energy wastage and higher bills. Instead, consider warmer clothing or blankets for a wallet-friendly way to keep warm.

Condensing Boiler Optimal Temperatures

Condensing boilers excel in efficiency by capturing nearly all heat from flue gases. To maintain this, the heat exchanger should operate at or below the dew point of around 55°C. This is the point at which water vapour condenses into liquid.

Setting Temperature on a Viessmann Boiler

Temperature control on a Vitodens 100-W - What temperature should my boiler be set at for hot water UK | BoilerhutAdjusting the temperature on a Viessmann boiler involves a few simple steps.

For radiator temperature:

  1. Press the MODE button until the radiator icon flashes,
  2. Then use the arrow keys to set your desired temperature
  3. Confirm with OK.

For hot water temperature:

  1. Press the MODE button until the tap icon flashes,
  2. Then use the arrow keys to set your desired temperature
  3. Confirm with OK.


Efficiently heating your home involves more than just cranking up the boiler. It requires a balanced approach to temperature settings across your system.

By adhering to recommended settings for boilers and water cylinders and making smart use of thermostats and valves, you can enjoy a comfortably heated home in an energy-efficient and cost-effective manner.

The Viessmann Vitodens 200-W range of boilers have built-in heating curves which, when correctly set, will keep your home warm all day with very little effort.

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