Optimal Boiler Temperature: How to Adjust Combi Boiler Flow

May 10, 2023 | News

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Increasing Boiler Efficiency by Adjusting Flow Temperature

One of the most effective ways to improve your boiler’s efficiency is by lowering the boiler temperature. Adjusting the flow temperature to the ideal setting can make your boiler more efficient, potentially reducing your heating bills by 6-8%. This article will guide you through the process of reducing your combi boiler’s flow temperature, discussing the types of boilers that allow adjustments, and providing other useful tips.

If you’re considering replacing your old boiler with a more energy-efficient one, check out our boiler replacement guide. Newer boilers can modulate down to 10% power output, significantly cutting energy costs.

Combi Boiler Flow Temperature: An Overview

The flow temperature refers to the water temperature achieved by your boiler before the water travels to your home’s central heating system. Most condensing gas boilers operate on an 80/60 flow and return temperature range.

Operating at 80/60 means the hot water temperature is 80°C when leaving the boiler and returns to the boiler at 60°C after circulating through the heating system. The hot water temperature drops because it has transferred 20°C of heat to your home’s rooms.

To achieve A-rated efficiencies, modern boilers need to operate at lower flow and return temperatures than 80/60.

Adjusting Flow Temperature: A Step-by-Step Guide

Identifying Your Boiler Type

First, you need to determine whether you have a condensing combi boiler. These boilers produce both hot water and heating. If you’re unsure, you can consult a Gas Safe engineer during your next boiler service or follow these simple guidelines:

  • If your boiler doesn’t use a hot water cylinder, it’s a combi boiler.
  • If it’s a condensing boiler, it will have a white pipe running to an outside or inside drain.
  • If your boiler was installed within the last 16 years, it’s most likely a condensing boiler.

Optimal Flow Temperature Setting for Combi Boilers

Generally, the optimal flow temperature setting for combi boilers is the lowest possible temperature. In older homes, this is usually 60-65°C, while newer homes typically have a flow temperature between 50-55°C.

The optimal flow temperature setting in your home depends on several factors, including insulation levels, radiator sizes, and thermostat temperature settings.

How to Reduce Combi Boiler Flow Temperatures

There are various methods to adjust your combi boiler’s flow temperature using the controls attached to your boiler. Below are three common ways to reduce the flow temperature and improve energy efficiency:

  1. Dials: Most boilers have two control dials, one for hot water flow temperature and another for the heating system. Turn down the dial with the radiator icon to the desired flow temperature, usually around 60°C for most homes.
  2. Digital Displays: If your boiler has a digital display, you can view and adjust the flow temperature using the radiator icon dial. This will only affect your heating system, not your hot water.
  3. Digital Displays without Dials: Some newer boilers have digital displays with plus/minus or up/down buttons. Use these buttons to lower the temperature setting on the display, ensuring you only select the heating temperature option.

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Special Cases: System Boilers with Hot Water Cylinders

System boilers with hot water cylinders can’t be lowered to the same temperatures as condensing boilers, so they can’t operate at maximum efficiency levels. If you have a system boiler with a hot water cylinder, you’ll need separate temperatures for heating and hot water, which requires contacting a heating engineer.

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