Over the past few years, like many people in the UK, I have become very interested in how much energy my home actually uses. Gas prices have been very volatile due to the conflict in Ukraine, and now with more conflict in Iran it looks like prices are expected to rise again.
Living in a Victorian house, which we are currently renovating, means I keep an extra eye on the heating bill. And, while our current setup works well, I’m starting to wonder if the way the boiler was set up is affecting the bills.
This Boiler flow temperature There is a boiler setting that the homeowner can easily control, and can affect how the boiler operates and the energy it uses. Here’s how I changed mine and what happened when I did.
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What is flow temperature and why does it matter?
Simply put, the flow temperature is the temperature of the hot water leaving the boiler and circulating around it heat emitterssuch as radiators. Conventional thinking is that higher temperatures lead to warmer temperatures radiators Quickly, and brings the room up to temperature quickly.
This means that when your boiler is installed, the plumber often sets the flow temperature to 70°C or occasionally 75-80°C.
But, new thinking suggests that running your gas boiler at a lower flow temperature can improve efficiency, especially with modern ones. Condensing boiler which is designed to recover excess heat from the exhaust gas.
Theory states that boilers actually run more efficiently when the water returning to the boiler from the radiators is relatively cold, around 50°C. Therefore, if the flow temperature is too high, the return temperature is also high, which means that the boiler spends less time operating in its most efficient condensing mode.
How I Adjusted My Flow Temperature
our Heating system Buxy 24Kw Ecoblue condensing gas boiler with cast iron column radiators and nest Smart thermostat. The system works well, but I wondered if it could work more efficiently.
I decided to try an experiment to see if the theory about flow temperature works in a real life situation. I adjusted the boiler settings to lower the flow temperature to 63°C, and ran the heating system as normal for the entire month of January 2026, to see if that made any measurable difference.
The thermostat schedule stayed the same and we generally heated the house just fine. This meant that the heating was on from 6.00am to 9.00am, again from 12.00pm-2.00pm, another burst from 4.00pm-6.00pm and then again in the evening from 9.00pm-11.00pm. This maintained a constant temperature between 19°C-21°C during the day and 18°C-19°C overnight.
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What happened when I changed my flow rate
Lowering the flow temperature definitely changed how the system behaved. Radiators do not release intense heat quickly after a boiler breaks down. Instead, they heated more slowly, and most importantly, the heating cycles lasted longer, but at a lighter level of output. I could also tell that the boiler was running in condensing mode, mostly because it was so quiet, which was an added advantage.
In theory, this is exactly what you want. A condensing boiler operating continuously at lower temperatures should be more efficient. But does this translate into real financial savings on our energy bills?
I tracked gas consumption through an app provided by my energy provider. It certainly looked down. And no doubt the house was more consistently warm.
I looked back on the app and was able to compare January usage over several years. This is a good month to test because it is usually the coldest and heating demand is high. The results were as follows:
- January 2026: 2,246 kWh
- January 2025: 2,412 kWh
- January 2024: 2,303 kWh
At first glance the 2026 looks a little better than the 2025, but not dramatically different from the 2024.
What do the results mean?
In summary, changes in flow temperature did not result in a large reduction in overall gas consumption. The difference between years was only a few hundred kilowatt-hours in a whole month.
At first this seemed disappointing, but we have to consider the difference in weather. 2025 was not a particularly cold winter, so that almost certainly accounts for part of the variation, as even small changes in average outdoor temperatures can alter heating demand.
In terms of real money, the difference in the years I measured was around £40 for months. This is still a good saving, but with gas prices at the start of 2026 lower than in the previous two winters, it is likely that cost comparisons are affected by changes in energy tariffs rather than boiler operation. So even if the gas bill looked better, the actual gas usage was the same.
So did lowering the flow temperature help? Probably a little, but not dramatically in terms of energy consumption and costs.
Should I keep my flow temperature low?
However, financial gain is not the end of the story. What clearly changed was how the heating system behaved. Instead of rapid bursts of heat caused by boiler shutdown, (short cycling) where the boiler and thermostat try to chase small 0.5°C increments, the system ran in long, steady cycles that are more efficient. This is also easier on long run boilers and is generally considered good practice, especially for condensing systems.
Another potential benefit is comfort. Low flow temperatures often produce more uniform indoor temperatures rather than sharp swings between hot and cold. Also seen in this Heat pump And Underfloor heating Set up
Consequently, I believe that adjusting the flow temperature is still worth trying, especially since it is simple and easily reversible. I leave my boiler at 63°C and I am happy with it.
I had hoped for greater savings, but in the end it became more about fine-tuning an already functioning system than achieving dramatic reductions in energy consumption.
The system continues to run reliably and comfortably at the lower setting, and the boiler is definitely running more smoothly. This is also evidenced by the pressure, which at 75°c often reaches 2.5 bar plus, while at 63°c it does not exceed 2.0 bar. This again puts less stress on the system and reduces risk Boiler problems or additional maintenance.
Overall, I am happy with the experiment as the house is consistently warmer and more comfortable. The bill is reduced – even if only slightly, and the boiler is operating more efficiently in its optimum range. The rewards for very little effort are very impressive and significant.
For more ways to reduce your energy bill, take a look Energy saving tipsfind out When to turn off your heating in the springAnd make sure your Draft-proofing The steps are all up to scratch.
