What temperature should a condensing boiler be set at?

Most modern boilers will have a digital dial that allows you to set the output temperature. For combi boilers, the recommended output temperature for the radiators is 75 °C and for the water is between 50 °C and 60 °C. You shouldn’t need to adjust these output temperatures as you may alter the boiler’s efficiency. Please note that for best efficiency with Viessmann boilers we would recommend weather compensation, this automatically adjusts the heating boiler flow temperature to the optimum temperature to external weather conditions.

The higher this temperature is set, the quicker your boiler will be able to heat your home. However, you may find that your heating bills increase and your boiler’s efficiency could decrease by around 10 or 20 per cent. The maximum temperature that we recommend you set your radiator output to is 80 °C.

If you have a conventional boiler system, your water cylinder will have its own thermostat. This is usually fitted on the side of the tank. You should set the temperature between 60 and 65 °C but for maximum efficiency, it should be set to around 60 °C. Do not set it lower than this as you could increase the risk of contracting Legionnaires’ disease. Legionnaires’ is a form of pneumonia that’s caused by bacteria in water. If the temperature of the water in your cylinder isn’t hot enough, the bacteria that causes the disease, Legionella pneumophila, can grow and you may be at risk. It’s worth noting that the temperature of the tap water should always be lower than the radiator output temperature.

You should utilise all of the controls in your heating system to ensure that your home is being heated in an efficient way. Your room thermostat should be set to around 18 to 21 °C. This is the most comfortable and healthy temperature for your home. Your bedroom should be slightly cooler than this at around 16 to 18 °C for the optimum night’s sleep. A programmable room thermostat should allow you to set separate temperatures for different rooms at varying times of the day.

Another way to control your heating is via thermostatic radiator valves (TRVs). A TRV will control the flow of water that passes through the radiator to change the amount of heat that it gives off. The TRV on each radiator should be set to number three, which will provide a room temperature of around 20 °C.

If you follow our recommendations above, your boiler should continue to heat your home efficiently.

When the weather starts to cool off, it can be tempting to turn up the TRVs, the room thermostat or even the boiler thermostat. However, in doing so, you could waste a lot of energy and your heating bills may increase. If your heating is on but you still feel cold, you should grab a pair of woolly socks to wear on your feet and an extra jumper. Blankets are a good idea for a cosy night in. Choosing to do this instead of increasing your heating system temperature is better for the environment, too. 

A condensing boiler is one of the most efficient types of boiler. This is because it is able to recover virtually all the heat from the flue gases and use this to heat your home. For the boiler to work at its most efficient, the heat exchanger needs to be equal to or below the dew point temperature. The dew point temperature is a measurement that determines the humidity of air and is the temperature at which water droplets form in the heat exchanger. For gas boilers, the dew point is around 55 °C. This means that the water needs to be 55 °C or lower for your boiler to maintain its efficiency. 

There are two temperatures that you’re able to select on your Viessmann boiler. One is the temperature of the water that flows through the radiators and the other is the temperature of the water that comes out of your taps.

To alter the radiator output temperature:

1. Step 2: Press the MODE button on the front of your Viessmann boiler. You’ll notice that the radiator icon flashes.
2. Step 3: Tap OK to select the radiator icon and then adjust the temperature using the up and down arrow keys.
3. Step 4: Press OK again when you’ve chosen your preferred temperature.

To alter the tap output temperature:

1. Step 2: Press the MODE button followed by the down arrow until the tap icon flashes.
2. Step 3: Touch OK to select it and then adjust the temperature using the up and down arrows.
3. Step 4: Tap OK once more to confirm the temperature.

Alternatively, you can watch the video below that demonstrates how to change the radiator output temperature.