Glow-worm Energy Combi Boiler Cost with Installation

The Glow-worm Energy combi has a lot to offer for its price bracket: with Quiet Mark approval; a 7-year standard warranty; and impressive hot water flow rates. Backed by the engineering of the Vaillant Group and manufactured in Derbyshire, it is a strong choice for homeowners who want a reliable, compact combi without stepping into premium pricing territory.

Here’s a breakdown of the specs for the Glow-worm Energy combi:

Glow-worm Energy Combi Product Table
	Available outputs	25kW	30kW	35kW
	Type	Combi	Combi	Combi
	Fuel	Gas	Gas	Gas
	Condensing	Yes	Yes	Yes
	Efficiency rating (%)	93	93	93
	ErP	A	A	A
	LPG compatible	Yes	Yes	Yes
	Standard guarantee	7 years*
	Max output (kW)	25	30	35
	Flow rate (l/min)	12.1	14.2	16.5
	Mounting	Wall-mounted
	Dimensions (mm)	700 x 390 x 280
	Typical price (incl. VAT)	£1,050	£1,100	£1,150
	Typical installation cost (incl. VAT)	£800 – £1,400
	Total cost	£1,850 – £2,550

*Terms and conditions apply.

Glow-worm Energy Combi overview

Glow-worm have been part of the Vaillant Group since 2001, which means German engineering, but the boilers themselves are still made in Belper.

What makes it worth looking at is a combination of things that don’t usually come together at this price: a 7-year warranty, Quiet Mark certification across all three output sizes, and at 280mm deep, a footprint that’s noticeably shallower than most of its direct rivals. The Vaillant ecoTEC Pro at 335mm. In a kitchen where the available cupboard depth is borderline, those 58mm can determine whether the boiler fits at all.

At 35kW the Energy delivers flow rates of 16.5 l/min, this is the highest in this price bracket, above what either the Worcester 4000 or the Vaillant Pro can manage at equivalent outputs. For homes where two bathrooms see simultaneous morning use it makes all the difference.

Glow-worm Energy Combi Range
Model output size	House size	Bathrooms	Radiators
25kW	Flats 1 to 2 bedrooms	1	Up to 12
30kW	Small homes 2 to 3 bedrooms	1-2	Up to 15
35kW	Small-medium homes 3 bedrooms	2	Up to 20

The 30kW is the model most installers reach for first when quoting a 3-bedroom home with one bathroom and a reasonable amount of radiators. The 35kW delivers 16.5 l/min, which is enough for two bathrooms in normal morning use.

Key benefits at a glance

• ErP A-rated efficiency (93%)
• Automotive-grade aluminium heat exchanger with patented 4-sided cooling
• Grundfos modulating pump 
• Quiet Mark certified across all three models
• Modern LCD display, easy to change settings
• Rear and top flue option for flexible installation
• Compact, cupboard-fit (700mm tall, 280mm deep)
• Compatible with Glow-worm MiGo, MiSet and Climastat smart controls
• Available as an LPG model
• 7-year warranty as standard out of the box*

Glow-worm Energy Combi technical specifications

The heat exchanger is “automotive grade aluminium”, which sounds like marketing but is a grade held to tighter manufacturing tolerances than standard cast aluminium. This quality of aluminum is: lighter, thermally more responsive, and engineered to handle repeated stress cycles without degrading. 

The patented 4-sided cooling geometry on the heat exchanger spreads heat more evenly during firing, reducing the peak thermal stress that causes microcracks in conventional single-sided designs over time.

It’s still aluminium, not stainless steel, but that’s the trade-off at this price. It is also why a Power Filter isn’t optional if you want the 10-year guarantee; sludge and limescale are what shorten aluminium heat exchangers, and a filter is the primary defence against both.

Output and efficiency ratings

All three models achieve an ErP efficiency of 93%. For a household upgrading from a non-condensing boiler, this will be a substantial improvement. For a household already running a modern condensing boiler, the reduction in running costs against their existing system will be real but modest.

Flow rates at ΔT30K are 12.1 l/min for the 25kW, 14.2 l/min for the 30kW, and 16.5 l/min for the 35kW. The 35kW’s 16.5 l/min is the highest in this price bracket — above the Worcester Greenstar 4000’s maximum at 30kW, and above the Vaillant Pro’s 12.3 l/min at the same output. For a home where two bathrooms are in regular simultaneous use, that figure is the one that should guide the output decision.

Dimensions 

All three models share the same dimensions: 700mm high, 390mm wide, and 280mm deep. The compact footprint means the Energy combi can be installed inside a standard kitchen cupboard, which is an increasingly common priority for homeowners looking to conceal pipework and maintain a clean interior look.

Components included

The Grundfos modulating pump is a step up from the standard fixed-speed pumps found in many boilers at this price. It reads system demand and adjusts flow rate continuously, which reduces energy consumption from the pump itself and prevents the overheating and pressure fluctuations that can occur when a fixed-speed pump is running in a lightly loaded system. Homeowners rarely notice it, but it contributes quietly to both running costs and system longevity.

Most combis can only be flued through the top or to the side. The Energy’s rear flue option means it can be installed hard against a back wall and flued directly through it, which opens up installation positions that would otherwise be impossible and removes the need for additional bends in the flue run.

The LCD display is bright and functional, with pressure gauge, heating and hot water temperature controls, and a reset switch.

For smart app control, the MiGo Link gateway connects the Energy to Glow-worm’s MiGo app, enabling remote heating schedules, energy monitoring, and weather compensation when paired with a compatible thermostat. It’s sold separately, as is the thermostat, so factor in an additional £100-£200 if app control is a priority.

Prices and installation costs

This price includes the boiler unit and a standard horizontal flue. 

A horizontal side-wall flue adds around £100–£150; a vertical roof flue can exceed £500 depending on your property’s configuration. 

Fitting a Glow-worm Power Filter at installation is the route to the 10-year warranty. The filter itself costs £80-£120, but it is also mandatory under UK Building Regulations regardless of warranty considerations, so the incremental cost for accessing the 10-year cover is marginal once the installation is underway.

Using a mid-range installation figure of £1,200:

Glow-worm Energy Combi Costs
Output size	Unit cost (incl. flue)	Total (incl. installation)
25kW	£1,050	£2,250
30kW	£1,100	£2,300
35kW	£1,150	£2,350

Warranty and support

The Energy comes with a 7-year warranty, but it needs to be registered within 30 days of installation to activate it. Without registration, cover reverts to just 12 months from the installation date – a significant drop that is easy to miss if your installer doesn’t raise it on the day. Your installer should complete this as part of handover, but it’s worth confirming it has been done before they leave.

This is a much simpler warranty to access than the Vaillant ecoTEC Pro, which starts at 2 years unless your installer is Vaillant Advance registered..

The 10-year warranty is available when the boiler is registered through Glow-worm’s myREWARDS programme by a Club Energy installer, with a Glow-worm Power Filter fitted and registered at the same time. This must happen at the point of installation as the 10-year warranty cannot be added retrospectively. 

The warranty covers manufacturing defects and component failure under normal use. It does not extend to damage arising from poor water quality, external gas or electricity supply faults, or poor system maintenance.

To keep either tier of warranty valid, the boiler must receive an annual service by a Gas Safe registered engineer with the Benchmark checklist completed at each visit.

Installation information

A standard installation typically costs around £1,200. 

The Energy has a well-established reputation among installers for being straightforward to install, being light enough to position on a high bracket without requiring two people, and at 280mm deep it fits into kitchen cupboards that would require modification for most of its rivals.

What to expect on installation day

Do you need a system flush or filter?

A magnetic filter is mandatory under UK Building Regulations. For the Energy specifically, a Glow-worm Power Filter also unlocks the 10-year warranty. A filter is fitted to the system to capture rust and dirt particles before they circulate through the boiler. This is an essential part in protecting internal components and supporting boiler longevity.

A powerflush is strongly recommended on systems over ten years old. Clean pipework protects the aluminium exchanger and keeps system efficiency stable over time

A system flush is carried out before the new boiler is installed. This removes sludge and debris before the new pipework is installed, and ensures your radiators heat evenly and reduces the risk of internal blockages.

Budget £350-£800 for a powerflush and £80-£120 for the Power Filter.

Finding a Gas Safe registered engineer

All gas boiler installations must be carried out by a Gas Safe registered engineer. 

For the 10-year warranty, your installer also needs to be a Club Energy member. 

Use the WhatPrice quote service to be matched with vetted, Gas Safe registered installers in your area, and ask at the quoting stage whether they hold Club Energy membership.

Reviews and ratings

Glow-worm have a 4.5-star rating on Trustpilot from over 7,000 reviews, with quiet operation and long-term reliability the most common reasons customers recommend it.

We’ve collated reviews relating to the Glow-worm Energy combi below:

Positive reviews

Quiet operation is the most consistently mentioned benefit across Energy combi reviews. One reviewer replacing a boiler that had woken them up every morning noted the Energy 25 was incredibly quiet in comparison and began heating their four-bedroom detached property far faster than the old system. Another with an Energy 35 described it as amazingly powerful and quiet, and a third praised the Energy 30 for being smart, efficient and quiet.

One installer replaced a 14-year-old Glow-worm CXi 30 with the Energy 30, and another noted the Energy 30 was a direct like-for-like replacement for its 15-year-old predecessor with identical flue mounting, making installation straightforward. A heating engineer reviewing from a trade perspective praised the Energy range’s rear flue option, easy service access, and quick warranty response, saying they always recommend Glow-worm to their customers.

The ten-year warranty is frequently cited as a source of reassurance, particularly given the price point.

Negative reviews

The most detailed negative account concerns an Energy 35 combi that required engineer attention five times in seven years, beginning with a manufacturing fault just two weeks after installation. The owner describes a pattern of engineers leaving the boiler in a worse state than they found it – including a leaking pipe joint and a water valve left turned off. The boiler failed completely just after the seven-year warranty expired, with the attending gas engineer noting the failure mode was unusual for a boiler of that age, and the reviewer had replaced a 25-year-old boiler that had run without issue.

Heat exchanger reliability is a concern that appears in more than one review. An Energy 25 developed a major leak from the heat exchanger at three years old, causing flooding and significant damage to kitchen units. A separate Energy 30 owner reports the primary heat exchanger began leaking from a weld at year seven, which they characterise as a manufacturing fault.

How the Glow-worm Energy Combi compares

Glow-worm Energy Combi Comparison Table
Model	Glow-worm Energy Combi	Worcester Bosch Greenstar 4000 Combi	Vaillant EcoTEC Pro Combi
Typical unit price	£1,100	£1,200	£1,050
Heat exchanger	Aluminium	Aluminium	Stainless steel
Standard warranty	7	7 Years	2 years
Max warranty	10	10 Years	10 years
Built-in WiFi	No	Yes	No
App control	MiGo	Bosch EasyControl	vSMART
Cupboard fit	Yes	Yes	Yes
Max output/bathrooms	35kW 2 bathrooms	30kW 1 & ensuite bathrooms	30kW 1-2 bathrooms

Keep in mind that this comparison focuses on key features, but there may be other details that matter more for your home. For personalised guidance on choosing the right boiler, we recommend speaking with a Gas Safe registered engineer.

Final thoughts – is the Glow-worm Energy combi right for you?

The Grundfos modulating pump is the component that separates the Energy from cheaper boilers. A standard fixed-speed pump runs at the same rate whether the system is heating one radiator or fifteen. The Grundfos reads demand and adjusts continuously, which means lower electricity consumption from the pump itself, more consistent temperatures through the house, and less thermal stress on pipework and valves over time. 

The heat exchanger is the part of the specification worth scrutinising most carefully before buying. With automotive-grade aluminium, 4-sided cooling, and large waterways, the boiler is made lighter and more tolerant of the kind of marginal pipework conditions common in older homes. The trade-off against the Vaillant ecoTEC Pro’s stainless steel exchanger is most relevant in hard water areas, where aluminium scales up faster. With a Power Filter fitted from the start and annual servicing, that risk is well managed in most parts of the country.

On smart controls, the Energy requires more planning than the Worcester Greenstar 4000, which has built-in WiFi and connects directly to the Bosch app without additional hardware. The Energy needs the MiGo Link gateway to enable app control, which is a separate purchase of around £80-£100. 

Paired with a MiGo Select or sensoCOMFORT thermostat, the app is useful but the out-of-box experience is a basic LCD display rather than anything connected. If remote control from a phone is a priority from day one, factor in the gateway cost or consider whether the Worcester 4000’s built-in connectivity is worth the price difference.

The flow rate at 35kW, 16.5 l/min, is the main selling point for larger homes. Neither the Worcester 4000 nor the Vaillant Pro can match it at the same output. For a home where two bathrooms are used in the same morning window, it’s a meaningful advantage. For a home with one bathroom, 30kW is the more efficient choice. 

FAQ