Glow-worm Boiler Guides
Still using a Glow-worm boiler? Here’s everything you need to know
Glow-worm boilers were installed in millions of UK homes between the 1970s and early 2000s.
Reliable and straightforward, they were a trusted name for decades, but most models now fall far below modern efficiency standards.
If your property still runs on an old Glow-worm boiler, you could be paying hundreds of pounds extra each year in gas. Many are also eligible for a free replacement under the ECO4 Scheme.
This page brings together every major Glow-worm boiler range, with detailed guides explaining:
Typical efficiency and running costs
The most common faults and symptoms
Whether parts are still available
How to qualify for a free A-rated upgrade
Choose your model below or explore by range.
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Glow-worm Boiler Guides Overview
Glow-worm Micron Boiler Guide
Specs, common issues, fixes, and efficiency tips.
View guide →Glow-worm Hideaway (40–120 Series) Boiler Guide
Known faults, maintenance steps, and upgrade advice.
View guide →Glow-worm Compact Range Boiler Guide
Troubleshooting, parts info, and performance tips.
View guide →Glow-worm Fuelsaver Mk1 & Mk2 Range Boiler Guide
Typical problems, fixes, and servicing pointers.
View guide →Glow-worm Fuelsaver Complheat Range Boiler Guide
Error symptoms, quick checks, and parts notes.
View guide →Glow-worm Fuelsaver Economy Plus Range Boiler Guide
Efficiency tweaks and reliability improvements.
View guide →Glow-worm Space Saver Mk1 & Mk2 Range Boiler Guide
Maintenance checklist and fix-by-symptom steps.
View guide →Glow-worm Space Saver RF & RFS Range Boiler Guide
Common RF/RFS issues and how to resolve them.
View guide →Glow-worm Space Saver B & F Range Boiler Guide
Lifespan tips, spares, and quick diagnostics.
View guide →Glow-worm Space Saver Complheat & KFB Range Boiler Guide
Servicing notes and fault-finding for both ranges.
View guide →Glow-worm Swiftflow Range Boiler Guide
Typical Swiftflow errors, fixes, and upkeep tips.
View guide →Glow-worm Economy Plus Range Boiler Guide
Efficiency boosts and troubleshooting advice.
View guide →Glow-worm Ultimate Range Boiler Guide
Known faults, parts, and maintenance routines.
View guide →Glow-worm Majorca Range Boiler Guide
Range overview, fixes, and service pointers.
View guide →Glow-worm Classic Wall-Hung (23C–80B) Boiler Guide
Wall-hung specifics, faults, and repair basics.
View guide →Glow-worm Floor-Standing 65–120 Series Boiler Guide
Servicing intervals and fault-by-fault fixes.
View guide →Glow-worm BBU (Back Boiler Units) Boiler Guide
Safety notes, repairs, and replacement options.
View guide →Are Old Glow-worm Boilers Still Safe to Use?
Most Glow-worm boilers still operating today are decades past their intended service life. While they were well-built and reliable in their time, they no longer meet modern safety or efficiency standards.
With age, key safety components like seals, flues, and thermocouples deteriorate, which increases the risk of carbon monoxide leaks and poor combustion. Older open-flued models also depend on proper ventilation, meaning a blocked or restricted flue could cause dangerous gases to build up inside the property.
If your Glow-worm boiler hasn’t been serviced in years or shows signs of soot, noise, or frequent cut-outs, it’s best to have it checked by a Gas Safe engineer. In many cases, it’s safer and more cost-effective to replace it with a sealed, A-rated boiler through the ECO4 Scheme.
Typical Efficiency of Glow-worm Boilers
| Range | Average Efficiency | EPC Band | Status |
|---|---|---|---|
| Space Saver | 70–75% | F | Discontinued |
| Fuelsaver | ≈70% | F | Discontinued |
| Ultimate | 75–78% | E | Discontinued |
| Micron | 78–80% | D–E | Discontinued |
| Compact / Classic | 77–79% | D–E | Discontinued |
Modern A-rated condensing boilers reach 90–94% efficiency, reducing gas use and household energy bills by up to 30%.
Free Glow-worm Boiler Replacement Under ECO4
The ECO4 Scheme is a government-backed program that helps UK homeowners replace old, inefficient boilers with modern A-rated systems at no cost. Because all Glow-worm non-condensing boilers fall below current efficiency standards, most qualify for funding through ECO4.
You could be eligible for ECO4 if any of the following apply:
You receive qualifying benefits such as Universal Credit, Pension Credit, or Child Tax Credit.
Your home has a low EPC rating (typically rated D to G) or a low household income below your local authority’s threshold.
Someone in your home has a health condition made worse by living in a cold or damp environment, including asthma, COPD, heart disease, limited mobility, or a weakened immune system.
Upgrading through ECO4 improves household safety, reliability, and comfort. A modern A-rated condensing boiler can cut heating bills by up to 30% and produce far fewer emissions. New systems are also quieter, cleaner, and easier to maintain, giving you efficient heating all year round.
Check your eligibility for a free ECO4 boiler replacement to see if your home qualifies.
Why This Hub Exists
This hub was created to make it easy for homeowners to find accurate, reliable information about Glow-worm boilers. Many people still have older Glow-worm models but aren’t sure how efficient they are, what problems to look out for, or whether it’s worth repairing or replacing them.
Here, you’ll find dedicated guides for every Glow-worm boiler range. From the classic Hideaway and Fuelsaver models to the later Micron and Ultimate systems. Each guide explains common faults, energy efficiency, repair options, and how to qualify for ECO4 funding.
Our goal is to give you a clear picture of your current boiler’s condition and help you take the next step toward a safer, more efficient heating system.
Ready to Replace Your Old Glow-worm Boiler?
If your home still relies on an old Glow-worm boiler, it’s likely costing you more than it should in gas bills and maintenance. Older systems typically operate at around 70% efficiency, meaning nearly a third of the energy you pay for is wasted through the flue.
Replacing your boiler through the ECO4 Scheme can significantly cut your energy costs while improving comfort and reliability. The process is simple — if your home meets the eligibility criteria, you can receive a full installation of a modern A-rated boiler at no cost.
Many homeowners across the UK have already upgraded their Glow-worm systems through ECO4, gaining a quieter, safer, and far more efficient heating setup.
Check your eligibility today and see if you qualify for a free A-rated replacement under the ECO4 Scheme.
Glow-worm Boilers – Frequently Asked Questions
Check the front panel or inside the casing flap for the data plate, it lists the exact model name (for example, Glow-worm Micron 50FF or Glow-worm Ultimate 80BF). If the sticker has worn off, compare your unit to the images in our range guides or look at your Gas Safe service record.
They were well-built, but most models are now 20 – 40 years old and lack modern safety sensors. Age-related wear, blocked flues, or corroded seals can raise the risk of carbon-monoxide leaks.
Annual servicing is essential or, if eligible, replacing it under ECO4 is the safest long-term option.
Some basic faults can be fixed, but most spare parts are discontinued. Even when reconditioned components are available, repairs often cost £250 – £400 each time. For many households, a free A-rated replacement through ECO4 is cheaper and more reliable than continued repair.
Most non-condensing Glow-worm models run at 70 – 79 % efficiency, wasting up to a third of the gas burned.
Modern condensing boilers exceed 90 % efficiency, cutting fuel bills by roughly 25 – 30 % and lowering carbon emissions.
Yes. Every Glow-worm range listed here – Micron, Hideaway, Compact, Fuelsaver, Economy Plus, Swiftflow, Ultimate, Majorca, Space Saver, BBU, Classic, and Floor-Standing 65–120 is non-condensing and therefore eligible if your household meets the ECO4 criteria (benefits, low income, or health route).
What Our Customers Have To Say
Read More Of Our Reviews On Trust Pilot
We’ve had some bad experiences with installers in the past, but Free Energy Savings was a breath of fresh air. They were helpful and patient, answering all of our questions about the ECO4 scheme and making sure we understood how it worked. The installation was done quickly and professionally, and the team was extremely respectful of our home.
- Jessica B
We were a bit unsure about how the ECO4 grant worked, but Free Energy Savings made everything so simple. The team explained every detail of the grant and the benefits from a new boiler installation. When it came time for the installation, they arrived right on schedule and worked hard to get everything set up. What impressed me most was the attention to detail….
- Amelia L
Free Energy Savings exceeded all of our expectations. From the moment we contacted them, they were responsive and informative. The team helped us through the paperwork for the ECO4 grant, which was a big help since we had no idea where to start. The installation crew was friendly, professional, and fast. It’s been a couple of months now, and we’re already…
