Glow-worm Ultimate3 Combi Boiler Cost with Installation

The Glow-worm Ultimate3 is a reliable, efficient combi from Glow-worm’s Belper factory, available in 30kW and 35kW outputs. It delivers 94% ErP efficiency, a Grundfos modulating pump, and an integrated filling loop at a competitive price point. 

The warranty starts at 5 years, extendable to 10 years through Club Energy with a Power Filter. The one practical limitation is size. Standing at 740mm tall and 300mm deep, it will not fit a standard kitchen cupboard.

Glow-worm Ultimate3 Combi Product Table
	Available outputs	30kW	35kW
	Type	Combi
	Fuel	Gas
	Condensing	Yes
	Efficiency rating (%)	94
	ErP	A
	LPG compatible	No
	Standard warranty	5 years
	Max output (kW)	30	35
	Flow rate (l/min)	12.4	14.4
	Mounting	Wall-mounted
	Dimensions (mm)	740 x 418 x 300
	Typical price (incl. VAT)	£1,000	£1,100
	Typical installation cost (incl. VAT)	£800 – £1,400
	Total cost	£1,800 – £2,500

*Terms and conditions apply.

Glow-worm Ultimate3 combi overview

The Glow-worm Ultimate3 combi is designed for medium to large homes that need a reliable, high-output boiler with strong hot water delivery. Built at Glow-worm’s Belper factory and available in 30kW and 35kW outputs, it is ErP A-rated at 94% efficiency and provides both central heating and hot water directly from the mains, without the need for a separate cylinder or storage tank.

As an all-in-one combi boiler, the Ultimate3 heats water on demand, which means hot water arrives quickly and there is no tank to run cold. Both models are fitted with a Grundfos modulating pump and an integrated filling loop, and both are compatible with Glow-worm’s MiGo smart control range.

Glow-worm Ultimate3 Combi Range
Model output size	House size	Bathrooms	Radiators
30kW	Medium to large homes, 3 to 4 bedrooms	1 & ensuite	Up to 15
35kW	Large homes, 4+ bedrooms	2	Up to 20

Choosing between the 30kW and 35kW comes down to how much your home draws on hot water at any given time. 

The 30kW delivers 12.4 l/min and is well-matched to a medium-to-large home with one bathroom and an ensuite, covering up to around 15 radiators. The 35kW delivers 14.4 l/min and is the model for two-bathroom homes where both showers or baths might run within the same morning window as it has the output to sustain that without flinching. If you have two bathrooms used simultaneously on a regular basis, the 35kW is the sensible starting point here.

Key benefits at a glance

• ErP A-rated efficiency (94%)
• Automotive-grade aluminium heat exchanger
• Grundfos modulating pump
• High hot water flow rates: 12.4 l/min (30kW) and 14.4 l/min (35kW)
• Integrated filling loop
• Built-in frost protection
• Quiet operation
• NOx Class 6 (low emissions)
• Flexible flue options including top and rear configurations
• MiGo app-based control compatible
• 5-year standard warranty, extendable to 10 years with Club Energy and Power Filter*

Glow-worm Ultimate3 combi technical specifications

Built in Belper as part of the Vaillant Group, the Ultimate3 is a reliable, efficient combi with strong hot water performance. Both models are ErP A-rated at 94% and fitted with premium components including a Grundfos modulating pump and integrated filling loop.

Output and efficiency ratings

At 94% ErP efficiency, the Ultimate3 converts nearly all the gas it burns into usable heat. As a condensing boiler, it recovers warmth from the flue gases that would otherwise be expelled outside. This recovered heat is what pushes efficiency beyond the 90% barrier that older non-condensing boilers could never reach. 

Both models carry a NOx Class 6 rating, which is the lowest nitrogen oxide emissions classification available for gas boilers. NOx is produced during combustion and contributes to air pollution; Class 6 indicates the Ultimate3 produces less than 56mg/kWh of NOx, putting it among the cleaner-burning gas boilers currently available. This matters increasingly for homeowners who want to minimise the environmental impact of a gas installation.

Dimensions 

At 740mm high, 418mm wide, and 300mm deep, the Ultimate3 is a larger boiler than most mid-market rivals. Standard kitchen cupboards are built to around 720mm internal height, so the Ultimate3 is already too tall by 20mm before depth is considered. 

This is not a limitation if the installation space is planned accordingly, but it needs to be factored in at the survey stage rather than discovered on installation day.

Components included

The Ultimate3 uses automotive-grade aluminium, held to tighter manufacturing tolerances than standard cast aluminium. The large-waterway design makes it more tolerant of older, less pristine pipework than narrower heat exchangers. In hard water areas it will scale faster than stainless steel, which is why the Power Filter is a meaningful accessory rather than an optional one.

The Grundfos pump adjusts its speed to match actual system demand. During quieter periods of hot water demand, it dials back output rather than running flat out. This reduces energy consumption from the pump itself over time and helps prevent the unnecessary pressure fluctuations that contribute to wear across the wider system.

When system pressure drops, most boilers require a separate filling loop to be attached to repressurise. The Ultimate3 has one built in, which means a homeowner can top up the pressure themselves without tools or an engineer visit, and the installer doesn’t need to factor in an additional accessory at the job.

The Ultimate3 is compatible with Glow-worm’s full MiGo controls range, including the MiGo Select smart thermostat and the MiGo Link internet gateway. Neither is included in the box, but the MiGo gateway, when paired with a compatible thermostat, enables remote control, weather compensation, and energy monitoring through the MiGo app. Smart controls are sold separately; budget around £100-£200 if app-based heating management is on the list.

Prices and installation costs

The Ultimate3 sits at the competitive end of the market for the performance it offers. At around £1,000 for the 30kW and £1,100 for the 35kW, it is competitive against similarly-sized combis from Worcester Bosch and Vaillant, both of which cost significantly more. 

Unit prices include the boiler and a standard horizontal flue. The flue, a critical component that safely directs combustion gases outside, is typically purchased alongside the boiler. 

A standard horizontal side-wall flue costs around £100, which is the most common option, but a vertical roof flue can cost up to £500 depending on the complexity of the installation. Note that the 35kW’s 6-metre maximum horizontal flue restriction may require a different flue configuration in some properties.

Here’s what to expect with a £1,200 installation cost:

Glow-worm Ultimate3 Combi Costs
Output size	Unit cost (incl. flue)	Total (incl. installation)
28kW	£1,000	£2,200
33kW	£1,100	£2,300

Warranty and support

The Ultimate3 comes with a 5-year parts and labour warranty as standard. To keep it valid, the boiler must be registered with Glow-worm and serviced annually by a Gas Safe registered engineer, with service records completed in the Benchmark logbook. Glow-worm will not cover faults caused by contaminated water, inadequate installation, or failure to maintain the annual service requirement.

The 10-year route requires a Club Energy registered installer and a Glow-worm Power Filter fitted and registered at the same time during commissioning. This cannot be added after the fact. For homeowners who want the 10-year cover, the question to ask at the quoting stage is whether the installer holds Club Energy registration.

The Power Filter also serves a practical purpose beyond the warranty: it captures metallic debris and sludge before it circulates through the heat exchanger, protecting the aluminium exchanger from the particulate contamination that shortens its life. It is a warranty condition, but it would be worth fitting regardless.

Installation information

When choosing a new boiler, it is useful to know what to expect from the installation process. Installation costs for the Glow-worm Ultimate3 combi are typically around £1,200, depending on the installer, local rates, your current heating system, and any additional parts needed.

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 Ultimate3, fitting a Glow-worm Power Filter also unlocks the 10-year warranty, so the filter serves both purposes at once. 

A powerflush is strongly recommended on systems over ten years old; the Ultimate3’s large-waterway heat exchanger handles older pipework better than tighter designs, but clean pipework is still the right starting position. 

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, the installer also needs to hold Club Energy membership. 

Use the WhatPrice quote service to be matched with vetted, Gas Safe registered installers in your area.

Reviews and ratings

Glow-worm holds a Trustpilot rating of 4.4 out of 5 from over 7,000 UK reviews. 

We’ve collated reviews specifying the Ultimate3 combi:

Positive reviews

The 10-year warranty is the most cited purchase driver among Ultimate3 reviewers, with several homeowners specifically noting it as the reason they chose this model over alternatives. 

The flow rate at 35kW is the other standout. One reviewer bought it explicitly for the 14.4 litres per minute hot water output and the 10-year guarantee, describing it as the two features that settled the decision. Another, upgrading from a 23-year-old boiler, said they were looking forward to years of trouble-free, cost-efficient heating and hot water. A third noted cost savings so significant the boiler would pay for itself in around 18 months compared with their previous system.

Quiet operation comes up repeatedly. Reviewers who switched from older boilers are frequently surprised by how little noise the Ultimate3 makes, one noted it was “much quieter” than their previous model. 

The controls get a positive mention too, described as simple even for homeowners who found technology a barrier with older boilers.

Negative reviews

Early faults appear frequently. One Ultimate3 30C owner had the boiler show an F28 error code the day after installation. Another had the boiler fail completely at 18 months, leaving the household without heating or hot water for over a week while warranty work was organised. A third reported four repairs over eight years, two under warranty (though Glow-worm’s response noted the boiler had never been serviced by their own engineers, which may have contributed to the fault pattern).

Heat exchanger leaks appear in multiple reviews. One homeowner had a heat exchanger start leaking at four years old, it was repaired under warranty, but the experience was frustrating regardless. Another reported a filling link failure at five years old, with Glow-worm initially declining to cover it under the 10-year warranty; this dispute highlights that warranty terms, particularly around what is and is not covered as a component failure, are worth understanding before purchase rather than during a claim.

The warranty registration pattern is also present here. Some negative reviews involve homeowners who discovered after installation that their cover was not what they had expected, either because Club Energy registration had not been completed, or because the servicing requirements had not been met. Asking the installer to confirm registration on installation day remains the most important single step a homeowner can take.

How the Glow-worm Ultimate3 combi compares

Glow-worm Ultimate3 Combi Comparison Table
Model	Alpha Evoke NX combi	Baxi 400 Combi 2.1 combi	Glow-worm Ultimate3 combi
Typical unit price	£800	£800	£1,000
Heat exchanger	Stainless steel	Stainless steel	Aluminum
Standard warranty	7 years	5 years	5 years
Max warranty	7 years	5 years	10 years
Built-in WiFi	No	No	No
App control	Alpha Connect (via OpenTherm)	Baxi uSense (sold separately)	MiGo (via gateway)
Cupboard fit	Yes	Yes	No (taller)
Max output/bathrooms	33kW 1-2 bathrooms	36kW 2 bathrooms	35kW 2 bathrooms

For personalised guidance on which model suits your home, we recommend speaking with a Gas Safe registered engineer.

Final thoughts – is the Glow-worm Ultimate3 combi right for you?

At £1,000 for the 30kW, the Ultimate3 costs around £200 more than the Alpha Evoke NX and sits at the top end of the Baxi 400 Combi 2.1’s price range. Neither rival is meaningfully weaker on output, the Baxi 400 Combi 2.1 goes to 36kW and the Evoke NX to 33kW, and both use stainless steel heat exchangers where the Ultimate3 uses aluminium. On raw specification, the Ultimate3 does not hold the stronger hand against either.

Where it does have an advantage is the warranty ceiling. The Evoke NX’s 7-year cover is its maximum, there is no extension route. The Baxi 400 Combi 2.1 tops out at 5 years. The Ultimate3 can reach 10 years through Club Energy with a Power Filter, which is a meaningful gap in long-term protection if the right installer is confirmed at the quoting stage. For homeowners who are focused on maximum warranty cover, that route is the clearest reason to choose the Ultimate3 over its rivals at this price.

The cupboard fit limitation is the most practical constraint. Both the Evoke NX at 255mm and the Baxi at 285mm will fit a standard kitchen unit; the Ultimate3 at 300mm deep and 740mm tall will not. For homes where installation space is a utility room, garage, or purpose-built housing, this is irrelevant. For homes where the boiler needs to go in a kitchen cupboard, the Ultimate3 is simply not the right model regardless of the other considerations.

On the points where all three are level: 94% ErP efficiency, NOx Class 6 emissions, and no built-in WiFi. None of the three includes smart connectivity out of the box, all require a separately purchased thermostat or gateway. 

The Ultimate3 and Evoke NX both use a Grundfos modulating pump, which is a strong component advantage over cheaper alternatives, while the Baxi uses its own pump. Built-in frost protection is present on the Ultimate3 and Evoke NX; the Baxi 400 Combi 2.1 relies on a pre-heated condensate trap rather than a full frost thermostat. Small differences at this price bracket, but worth knowing.

FAQ