Glow-worm Floor-Standing Boiler Range (65–120 Series) Guide
Apply Now For A Free Boiler Grant
Fill out the form below to take advantage of the free boiler grant.
By submitting this form, you consent to us contacting you by phone, SMS, or email regarding your ECO4 Free Boiler Grant application. We will not use your details for unrelated marketing. See our Privacy Policy for more. You can opt out at any time.
3 Step Eligibility Process
Complete Online Form
Fill out our quick online form to apply for your free boiler grant.
Get a Survey
Schedule a free home survey to assess your current boiler and energy needs
Get a Free Boiler Replacement
Receive a grant for a brand new, energy-efficient boiler at no cost.
Overview of the Glow-worm 65–120 Series Boiler Guide
The Glow-worm Floor-Standing boilers were once a staple of central heating across the UK. Built during the late 1980s through the early 2000s, models in the 65–120 Series became popular in larger homes and small commercial properties that needed dependable heating output and long-lasting performance.
This range included models such as the Glow-worm 65–80B, 85–100B, and 105–120B, each offering robust heat production and a simple, mechanical design. Many are still in operation today, which is a testament to their build quality. However, their age and non-condensing technology mean they are now outdated in both efficiency and safety compared to modern boilers.
This guide explains how these boilers perform today, what issues typically arise with the Glow-worm 65–120 Series, and what options are available if you’re thinking about upgrading through the ECO4 boiler grant scheme.
Key Specifications
The Glow-worm Floor-Standing series was designed for homes and small businesses that needed high heat output and reliability. Unlike wall-hung models, these boilers were installed at ground level, often in utility rooms, garages, or cupboards with ventilation space.
Main models include:
- Glow-worm 65–80B – A compact but powerful heat-only boiler suited to medium-sized homes.
- Glow-worm 85–100B – A mid-range unit offering higher output for larger heating systems.
- Glow-worm 105–120B – The most powerful model in the range, often used in bigger homes or small commercial spaces.
Technical overview:
- Type: Conventional (heat-only) boiler
- Fuel: Natural gas
- Flue type: Open or balanced flue depending on model
- Efficiency: Around 70–78% (Band E–F)
- Output range: 19–35kW (65,000–120,000 BTU)
- Controls: Basic thermostat and manual timer
- Installation period: Late 1980s to early 2000s
- Expected lifespan: 15–20 years
These boilers were designed with thick cast-iron heat exchangers, manual gas valves, and simple electrical circuits. They were built for endurance rather than refinement. But because every model in this range is non-condensing, much of the heat escapes through the flue. That inefficiency, combined with aging components, makes the Glow-worm 65–120 Series costly to run by modern standards.
Efficiency and Running Costs
When the Glow-worm Floor-Standing range first appeared, it was seen as an efficient and reliable solution for larger homes. At the time, a boiler operating at 75% efficiency was considered good performance. However, after thirty years of service, most models in this series now operate closer to 68–72% efficiency.
By contrast, a modern A-rated condensing boiler runs at 90–94% efficiency. The difference is significant. These older systems waste around a quarter of the gas they burn.
Estimated annual cost comparison:
- Large detached home: ~£1,250 per year with a 105–120B model, ~£850 with a modern boiler
- Medium home: ~£950 with a 85–100B, ~£650 with a new A-rated replacement
- Small detached or semi: ~£800 with a 65–80B, ~£540 with a condensing system
Those savings can add up to £300–£400 every year.
Beyond efficiency, these boilers also lack modulation and weather compensation. They work in a simple on-off cycle, which wastes energy and causes temperature swings. For homeowners still relying on a Glow-worm 65–120 Series boiler, the age of the system and the lack of replacement parts make upgrading a sensible long-term decision.
Common Issues and Fixes
The Glow-worm Floor-Standing boilers were built to last, but decades of operation have taken their toll. Many systems are still in use, but reliability has dropped sharply. Below are the most common problems seen across the 65–80B, 85–100B, and 105–120B models, with a look at how they’re usually resolved.
Boiler not firing or locking out
A frequent problem, especially in the 85–100B and 105–120B models. You might hear the boiler attempting to ignite but failing to light the burner. This can be due to a worn gas valve, a faulty ignition electrode, or a failing control PCB. Because original components are no longer produced, engineers often resort to refurbished parts. These may restore function temporarily but are not a long-term fix.
No heating or poor heat output
If radiators remain cold even when the boiler is on, the issue is often due to a seized pump or a blocked heat exchanger. Over years of use, sludge accumulates in the system and restricts flow. Engineers can flush the system and clean the heat exchanger, but performance rarely returns to normal. Larger models like the 105–120B tend to suffer most due to their heavy cast-iron components.
Overheating and kettling noises
A loud boiling or rumbling sound coming from the boiler indicates scale buildup. This problem is common in hard water areas and affects all models in the series. Over time, mineral deposits form on the heat exchanger, causing hot spots that boil water unevenly. Engineers may try chemical flushing, but in older boilers the problem usually returns quickly. Continuous overheating can damage the thermostat and pump.
Fan or flue faults
Many 85–100B and 105–120B boilers use a fan-assisted flue. When the fan bearings wear out or the air pressure switch fails, the boiler shuts down for safety. Replacement fans for these models are now obsolete. Engineers may adapt modern fans, but reliability is uncertain and installation costs are high.
Leaks and corrosion
Internal leaks are common in floor-standing boilers because of constant temperature cycles and vibration. Seals, pipe joints, and pump housings eventually weaken. In the 65–80B and 85–100B, corrosion often appears near the combustion chamber and condensate areas. Even small leaks can cause electrical faults and safety lockouts.
Ignition and pilot light problems
Older 65–80B units often use a permanent pilot light. If it goes out frequently, the issue is usually a worn thermocouple or pilot assembly. Dirt and carbon buildup around the flame sensor are also common. Replacing or cleaning these parts can restore operation temporarily, but long-term reliability is poor.
Blocked flue or poor ventilation
As these boilers vent through chimneys or horizontal flues, any blockage can restrict airflow and cause incomplete combustion. Signs include yellow flames, black soot, or a faint gas smell. This issue should always be treated as a safety concern. If any of these symptoms appear, the boiler must be switched off and checked by a Gas Safe registered engineer.
Parts discontinued
Every model in this series suffers from discontinued parts. Control boards, gas valves, and fans are no longer made by Glow-worm. Some refurbished parts can be sourced, but they are expensive and often fail within months. This lack of reliable spares makes ongoing repair increasingly impractical.
Summary
The Glow-worm 65–120 Series was known for durability, but time and corrosion have caught up. Frequent breakdowns, high gas usage, and poor efficiency make replacement the only practical long-term solution for most households.
Repair vs Replacement
While repairing a Glow-worm Floor-Standing boiler may seem cheaper in the short term, most repairs are temporary. Components are worn, spare parts are scarce, and repair costs add up quickly.
Typical repair costs:
- Ignition electrode or thermocouple: £100–£150
- Pump replacement: £250–£350
- Gas valve or PCB: £300–£450 (if available)
- Heat exchanger or major seal repair: £400+
The total cost of maintaining these boilers can exceed £500 per year once breakdowns become frequent. Meanwhile, gas usage remains high because of inefficiency.
Modern A-rated condensing boilers not only use less fuel but also come with long manufacturer warranties. Most homeowners find that replacement pays for itself through lower bills and fewer call-outs. Because the 65–120 Series is fully non-condensing, it qualifies for replacement under the ECO4 boiler grant if household criteria are met.
Alternatives and Modern Replacements
For homes upgrading from a Glow-worm Floor-Standing boiler, the Ideal Logic range is one of the most practical replacements. It offers compact dimensions, efficient performance, and compatibility with modern control systems.
Key advantages:
- Over 90% efficiency (A-rated)
- Wall-mounted, freeing up floor space
- Quiet operation and easy servicing
- Compatible with smart thermostats
- Long manufacturer warranties available
For larger properties, the Worcester Bosch Greenstar range is another strong option. These boilers deliver powerful heating output while maintaining high efficiency and reliability.
Between the two, the Ideal Logic range is often the best fit for replacing Glow-worm 65–120 Series boilers. Its size, versatility, and energy efficiency make it ideal for older properties transitioning away from heavy floor-standing systems.
Free Boiler Grant Eligibility
All Glow-worm Floor-Standing models, including the 65–80B, 85–100B, and 105–120B, qualify for replacement through the ECO4 boiler grant. These units are non-condensing and fall within the lowest energy bands, meaning they meet the technical criteria automatically.
Eligibility routes:
1. Health Route
If someone in your household has a health condition made worse by cold living conditions, such as high blood pressure, asthma, COPD, heart conditions, limited mobility, or a suppressed immune system, your home could qualify under ECO4’s health-based criteria.
Some councils also offer LA Flex, which allows broader eligibility for households that narrowly miss standard requirements.
2. Low-Income Route
Households with an EPC rating of D to G or a low annual income below the local threshold may also qualify even without benefits.
3. Benefits Route
You may qualify if you or someone in your household receives:
- Universal Credit
- Pension Credit
- Child Tax Credit
- Working Tax Credit
- Income Support
- Income-Based Jobseeker’s Allowance (JSA)
- Income-Based Employment and Support Allowance (ESA)
If your home still relies on a floor standing model, such as a 65-80b, 85-100b, or 105-120b, you likely meet the technical requirements for ECO4 replacement.
Is It Time to Replace Your Glow-worm 65–120 Series Boiler?
The Glow-worm Floor-Standing 65–120 Series was built to last, and for many years, it did exactly that. These boilers provided steady heating and reliability for countless homes across the UK. But with efficiency ratings below modern standards and spare parts now impossible to find, their time has passed.
Replacing your old Glow-worm boiler with a new A-rated system will improve efficiency, safety, and comfort while reducing energy bills.
If your home still uses a Glow-worm 65–120 Series boiler, it may qualify for a free replacement under the ECO4 grant. Upgrading now means fewer breakdowns, lower running costs, and reliable heat for years ahead.
Frequently Asked Questions
It is a floor-standing, heat-only boiler designed for larger homes and small commercial premises.
From the late 1980s through to the early 2000s.
They run at around 70–78% efficiency, compared to over 90% for modern condensing boilers.
Most parts are discontinued. A few refurbished components may be available, but reliability is low.
They can be safe if serviced regularly, but open flues, corrosion, and age increase risk over time.
The Ideal Logic range is often the most suitable due to its compact design, high efficiency, and straightforward installation.
The Ideal Logic range is usually the most suitable due to its size, compatibility, and high efficiency.
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…
