Watch the video above for a visual walkthrough, then read on for a fuller explanation.
What is flow temperature?
Your combi boiler heats water and sends it out to your radiators. The flow temperature is simply how hot that water is when it leaves the boiler and enters your heating pipes.
Many boilers leave the factory set to 70–80 °C or higher. That is hotter than most homes actually need. Turning it down is one of the easiest ways to save gas — and it costs nothing.
Do you have a condensing combi boiler?
This guide applies to condensing combination boilers — the type fitted in most UK homes since the mid-2000s. You can check in two ways:
- Look underneath the boiler — condensing boilers have a white plastic condensate pipe (around 21–32 mm) coming out below the unit. It may run to an internal waste pipe or disappear through the wall to drain outside.
- Check the manual — look up your boiler model at BoilerManuals.com and confirm it is a condensing appliance.
If your boiler is an older non-condensing model, the savings from lowering flow temperature will be much smaller. This guide is aimed at modern condensing combis without a hot water storage cylinder.
Why does a lower flow temperature save money?
Condensing boilers have a clever trick: they can squeeze extra heat out of the exhaust gases before they leave through the flue. This only works when the water returning to the boiler is cool enough — below around 54 °C (the dew point).
When the boiler is condensing, efficiency jumps from roughly 85–88% up to 90–98%. That extra efficiency comes free — you get more heat from the same amount of gas.
The key insight: if you set your flow temperature to 55 °C or below, the return water will almost certainly be below 54 °C, keeping the boiler in condensing mode for most of its running time. Industry estimates suggest this can save up to around 8% on your heating gas bill.
A simple analogy
Think of your boiler like a car engine. Running it at high revs all the time uses more fuel than cruising at a lower speed. A high flow temperature forces the boiler to work harder and dump more heat up the flue. A lower flow temperature lets it cruise efficiently.
Why it also improves reliability
Lowering flow temperature is not just about saving money — it is gentler on the boiler and the whole heating system:
- Less thermal stress — cooler water means less expansion and contraction in pipes, joints, and the heat exchanger over thousands of heating cycles.
- More condensing time — the boiler runs in its most efficient, designed operating mode rather than blasting at maximum temperature.
- Longer, steadier burns — the boiler cycles on and off less aggressively, which reduces wear on the ignition components, fan, and pump.
- More even heating — radiators warm up gradually and the room thermostat has time to react, avoiding overshoot where the house gets too hot and then cools down again.
Your home may take slightly longer to reach temperature after a cold start, but it will heat more evenly and the boiler will work less hard to maintain comfort once warm.
How to change your flow temperature
Every boiler brand does this differently. Some have a dial on the front; others use buttons and a digital display; some require access through a service menu.
- Find your boiler's user manual (try BoilerManuals.com if you do not have a paper copy).
- Look for "heating flow temperature", "CH temperature", or "radiator temperature" in the settings — this is separate from the hot-water temperature for your taps.
- Reduce the setting in small steps — try 60 °C first, then 55 °C if the house still warms up comfortably.
- Give each change a day or two before adjusting again, so you can see how the house responds in real weather.
The video above shows the process on a Vaillant ecoTEC plus with four buttons. Your boiler may look different, but the principle is the same.
Important: only adjust settings you understand. If you are unsure, ask a Gas Safe registered heating engineer during your next service — it takes only a few minutes.
The two-step strategy: winter and summer
Not every home warms up quickly enough on the coldest winter days at 55 °C. If that sounds like your property, use a two-step flow temperature strategy:
- Winter (cold weather) — use a higher flow temperature, perhaps 60–65 °C, so the house reaches a comfortable temperature on the coldest days.
- Spring, summer, and autumn — drop to 55 °C or below when outdoor temperatures are milder and less heat is needed.
If your home warms up comfortably at 55 °C or below all year round, you can leave it at that setting permanently — no two-step strategy needed.
Set a reminder on your phone to adjust the flow temperature when the seasons change, or ask your engineer to set it during the annual service.
A bonus: heat pump readiness
Homes that heat comfortably at 55 °C flow temperature or below are generally well suited to a future heat pump, which also runs at lower temperatures than a traditional boiler. If you are considering a heat pump later, getting your flow temperature down now is good preparation — a heat pump system designer can confirm suitability.
One caution: condensate pipe freezing
When your boiler condenses more (which happens at lower flow temperatures), it produces more condensate water. This drains away through the white plastic pipe underneath the boiler.
In very cold weather, an external condensate pipe that is uninsulated or poorly routed can freeze, shutting the boiler down. This is most common during severe cold snaps. If your condensate runs outside, make sure it is properly insulated and has a continuous fall to the drain. See our installation best practice guide for condensate guidance.
Go further with smart controls
Manually setting your flow temperature is a great first step. For automatic, ongoing savings, consider controls that talk directly to the boiler and adjust flow temperature based on how warm it is outside:
- Weather compensation — the boiler automatically lowers flow temperature on milder days without you changing anything.
- OpenTherm controls — modulating thermostats (such as certain Tado, Honeywell, or Drayton models) tell the boiler exactly how much heat is needed, keeping flow temperature as low as possible. See OpenTherm boilers and controls on MyBoiler.com.
- Manufacturer smart controls — many boiler brands offer their own weather-compensated controls designed to work with their appliances.
These advanced methods do the two-step strategy automatically, every day, without seasonal manual adjustments. Read more about modulating A-rated boilers with smart controls on MyBoiler.com.
Quick reference
- What to change: heating flow temperature (not hot-water temperature for taps)
- Target: 55 °C or below for maximum condensing; 60 °C as a sensible starting point
- Potential saving: up to around 8% on heating gas
- Side benefit: less wear on boiler components; more even comfort
- When to go higher: only if the house will not warm up on the coldest winter days
See also our sizing & efficiency guide for broader optimisation advice, and reducing flow temperature for combi savings on MyBoiler Hub.
Guide based on the MyBoiler video on flow temperature. Adjusting boiler settings is straightforward for most homeowners, but consult a Gas Safe registered engineer if you are unsure. This page does not cover hot-water (tap) temperature settings.