What Temperature Should Your Boiler Be?

If your heating bill makes you break out in a cold sweat, it could be time to adjust your boiler’s flow temperature.

But what temperature should your boiler be?

As you’d expect, the answer to “What temperature should your boiler be?” varies due to multiple factors.

But before discussing these factors, let’s define your boiler’s flow temperature.

What Does Your Boiler’s Flow Temperature Mean?

Your boiler’s flow temperature refers to how hot the water is when it leaves the boiler and travels through your central heating system to warm your home.

Usually, a new boiler’s factory setting is called 80/60 flow.

This fraction indicates that the water leaving the boiler, called the flow, is 80°C. The second half of the fraction is water returning to the boiler, called the return, at 60°C. In this example, 20°C of heat was given off into the room.

However, the factory setting of 80/60 flow and return temperatures is too high for condensing gas boilers to achieve their A-rated efficiencies displayed on the box.

Most condensing boilers need a flow temperature set around 55°C to 60°C to achieve their promised efficiency levels. This allows the boiler to recover heat from the exhaust gases.

But if you need to heat a space quickly, setting the flow temperature higher will help. However, it will be costly.

Generally, radiators will require higher flow temperatures, while underfloor heating systems work better with lower temperatures.

If you’re uncertain how to reduce your flow temperature, ask your Gas Safe registered engineer. But generally, it’s straightforward on combination (combi) boilers.

How To Reduce Your Boiler’s Flow Temperature

Lowering your boiler’s flow temperature will improve its efficiency. Here’s a quick step-by-step for the layperson to follow:

Step 1: Check What Boiler Type You Have

There are three different types of boilers:

• Combi boilers are the most common in many homes, providing instant hot water and heating.
• System boilers combine a hot water tank (cylinder) and the boiler to provide heating and hot water for your home.
• The third is a conventional boiler, or a regular boiler, which is commonly used in traditional heating systems. It is designed to heat radiators and produce hot water for taps through a separate hot water cylinder.

If you plan to reduce your flow temperature, consult your unit’s manual to ensure it can handle the change.

Most modern or condensing boilers can handle the reduced flow rate.

Step 2: Locate The Flow Temperature Control

Depending on the model or brand of your boiler, your flow temperature control interface can vary. Currently, flow temperature controls come in:

• Dials
• Digital display
• Or a control panel (sort of a combination of both)

These control panels will generally be labelled “CH Flow Temp” or “Heating Temperature.”

Again, we strongly suggest double-checking these control functions using the boiler’s manual.

Step 3: Reduce The Flow Temperature

As we’ve mentioned, various types of interfaces on many different boilers allow you to adjust the flow temperature.

For dials, there are usually two of them. One dial is for hot water while the other is for the heating system and will have some sort of visual representation to indicate which does what.

For example, a radiator icon represents the heating system, and a tap represents hot water.

While some manufacturers will have temperatures on their dials, some have decided to rank the heat between one and six. If you cannot find the solution to these numbers, most boilers must operate between 30°C-80°C.

Make sure to allocate a temperature (for example, 1 is 30°C and 2 is 40°C) to each number, with six being the top temperature.

If the dial has an “e,” you can assume that this is the boiler’s economy mode. Again, the temperature of this economy mode will change depending on the model and brand.

To adjust these systems, you just need to dial in the desired temperature.

A digital display allows you to monitor the temperature adjustments on the screen. The controls for this digital display can also be dialled or pushed buttons.

With a control panel, you must hold a function key that activates the flow temperature function.

Step 4: Check It Worked

Once you’ve set your desired temperature, you will want to check that the adjustments worked. Feel if the radiators are warming up correctly and are not scalding.

If you’ve adjusted the temperature to activate your boiler’s condensing mode, make sure you can see that it has been activated.

Lastly, when you’re happy, ensure the new temperature is comfortable to live with.

Now that we’ve reviewed the basic steps to adjust your boiler’s flow temperature let’s discuss the best temperatures.

Sidenote: Legionella Bacteria

Be aware of legionella bacteria, which is a naturally occurring microorganism that thrives in man-made water systems, including your home’s boiler. If the temperature in your system is between 20°C and 45°C, this bacteria becomes dangerous and can be inhaled.

To prevent this bacteria from developing, make sure to:

• Maintain your water’s temperature above 60°C and below 20°C to stop growing.
• Make sure to flush out stagnant water from water storage by running the taps in bathrooms that are not in regular use.
• Ensure that your heating system is descaled annually, as built-up lime scale is excellent for bacteria to reproduce in.

If you’re ever concerned, call your Gas Safe registered engineer to do some tests.

Best Temperatures For Your Boiler

The best temperature for your boiler is one you’re comfortable with, as these are all just general suggestions.

You can change your boiler’s flow temperature when necessary, which means turning it up for winter and down for summer.

Installing a smart thermostat can also simplify this task. You can adjust your heating system via your smart device or set a calendar reminder to change it.

But here are our best temperature suggestions:

Central Heating

Your home’s radiators require loads of heat energy to warm them up efficiently.

While many suggest setting the temperature between 75°C and 80°C for all types of boilers, lower the temperature to 60°C or 65°C for a longer run time.

At this temperature, your home will gently heat up, and your condensing boiler (all combi boilers are now condensing boilers) will function most efficiently.

If your home has underfloor heating, a lower temperature between 35°C and 50°C is high enough to effectively warm the property.

Hot Water

You want to prevent the growth of Legionella in your hot water supply by setting your combi boiler to between 43°C and 48°C.

In fact, it has been a legal requirement to limit hot water at bath taps to 48°C since 2010.

While a low temperature will still kill off the bacteria and prevent you from being scalded, setting your hot water temperature too high can be dangerous.

According to the Children’s Burns Trust, it only takes one second to get a deep burn in hot water when the water temperature is at 70°C.

If you have a system boiler that has held hot water for some time, you will want to set the temperature slightly higher or at the legal limit of 48°C.

For those with children, make sure to exercise caution when running them a bath, such as:

• Running cold water before the hot
• Testing the temperature with the back of your hand
• And always monitor your children around bath time

You can also install thermostatic mixing valves (TMVs) on your home’s faucets, which automatically control the temperature of the hot tap.

However, if you’re concerned about accidentally resetting your boiler’s temperature too high, call a professional.

When Unsure, Chat With A WarmZilla Professional

At WarmZilla, our entire team of professionals is waiting to answer your questions and are ready if you need someone to walk you through resetting your boiler.

Or book a Gas Safe registered engineer to reset your home’s boiler’s temperature.