Baxi 800 System 2 Boiler Cost with Installation

The Baxi 800 System 2 is Baxi’s top-of-the-range system boiler – the one that comes with a 10-year parts and labour warranty as standard, the Adey MagnaClean Micro2 filter already in the box, and a stainless steel heat exchanger that most rivals at this price point don’t include.

It’s available in 15kW, 18kW, and 24kW, shares the same compact 285mm-deep footprint as the 600 System 2, and is compatible with the Megaflo Eco cylinder range for homeowners who want a matched Baxi system from boiler to tank. If you’ve been weighing up the 600 System 2 versus the 800, the extra £250 buys you three more years of warranty and the filter without a separate purchase.

Discover more of the Baxi 800 System 2 specifications below:

Baxi 800 System 2 Product Table
		815 (15kW)	818 (18kW)	824 (24kW)
	Available outputs	15kW	18kW	24kW
	Type	System	System	System
	Fuel	Gas / LPG	Gas / LPG	Gas / LPG
	Condensing	Yes	Yes	Yes
	Efficiency rating (%)	93	93	93
	ErP	A	A	A
	LPG compatible	Yes (no kit)	Yes (no kit)	Yes (no kit)
	Standard guarantee	10 years
	Max output (kW)	15	18	24
	DHW flow rate	Determined by cylinder
	Mounting	Wall-mounted
	Dimensions (mm)	700 x 395 x 285
	Weight	29.5kg
	Filter included	Adey MagnaClean Micro2
	Typical price (incl. flue)	£1,100	£1,150	£1,300
	Typical installation cost (incl. VAT)	£1,500
	Total cost	£2,600	£2,650	£2,800

*Terms and conditions apply.

Baxi 800 System 2 overview

A system boiler heats water and stores it in a separate hot water cylinder – multiple bathrooms can draw simultaneously without the flow rate ceiling of a combi. The 800 System 2 does this with the full Baxi 800 specification behind it: stainless steel heat exchanger, brass hydraulics, Adey Micro2 filter in the box, and a 10-year warranty that doesn’t require a premium installer tier.

Three outputs cover the full range of typical UK family homes. The 815 suits smaller properties with an existing cylinder. The 818 is the standard choice for a three-bedroom home. The 824 covers larger properties with higher heat demand. All three share identical dimensions and the same included filter – the only meaningful step up between them is output capacity.

Baxi 800 System 2 Range
Model	Suitable for	Radiators	Notes
815 (15kW)	Small homes, 1-2 bedrooms	Up to 10	Best for smaller properties with an existing cylinder
818 (18kW)	Medium homes, 3 bedrooms	Up to 15	The most commonly fitted model
824 (24kW)	Larger homes, 3-4 bedrooms	Up to 20	For properties with higher heat demand

Output selection for a system boiler is based on your property’s heat loss, not the number of bathrooms – the cylinder handles hot water capacity separately. Your Gas Safe engineer will confirm the right output at survey stage. For most three-bedroom homes, the 818 is where you start.

Key benefits at a glance

• ErP A-rated efficiency (93% efficient)
• Stainless steel heat exchanger
• Brass hydraulics throughout
• 10-year parts and labour warranty as standard
• Adey MagnaClean Micro2 filter included in the box
• Compatible with Megaflo Eco cylinder range and Baxi cylinder range
• LPG compatible via software conversion – no kit, no extra cost
• Built-in pipe concealment bracket for a clean installation
• Front-access servicing
• Backlit LCD display with twist controls
• OpenTherm compatible
• IFOS weather sensor compatible for weather compensation
• Pre-heated condensate trap – reduces winter freeze risk
• External analogue pressure gauge for easy self top-up
• Fully modulating burner
• Central top flue with options up to 20m
• Hydrogen blend ready (up to 20%)

Baxi 800 System 2 technical specifications

What separates the 800 from the 600 in the Baxi system boiler range isn’t size or output – both come in the same three outputs, share the same footprint, and use the same stainless steel heat exchanger and brass hydraulics. The difference is the warranty and the included filter. The 800 gives you 10 years as standard; the 600 gives you 7. The 800 includes the Adey Micro2 filter in the box; the 600 requires a separate purchase. Everything else is broadly the same platform.

Output and efficiency ratings

All three models run at 93% efficiency, ErP A-rated. As condensing boilers, they recover heat from exhaust gases that older non-condensing boilers vented outside – which is why homeowners replacing a pre-2005 installation often notice their bills drop within the first few months.

The fully modulating burner is the everyday superpower here. It adjusts output to match what the system actually needs rather than cycling on and off at full power. Less wear, more even heat distribution, and better efficiency during the quieter parts of a heating season. Pair it with an OpenTherm thermostat like the Baxi uSense 2 and the boiler and thermostat communicate directly, making the modulation even more responsive to actual room conditions.

Dimensions

700mm tall, 395mm wide, 285mm deep – identical to the 600 System 2. At 29.5kg, two engineers lift it into position without difficulty. The built-in pipe concealment bracket routes connections neatly behind the casing, which matters in cupboard installations where appearances count. Front-access servicing keeps annual maintenance straightforward without moving the boiler off the wall.

What’s under the casing

The stainless steel heat exchanger is the component that earns the most attention when installers compare the 800 to rival system boilers at this price. Stainless steel handles limescale build-up better than aluminium in hard water areas – broadly the South East, East Anglia, the Midlands, and parts of Yorkshire – and is more resistant to the acid condensate produced during the condensing process. It’s a meaningful long-term advantage, and one that the Viessmann Vitodens 050-W also offers but most rivals at this price do not.

The Adey MagnaClean Micro2 filter is included in the box and must be fitted and registered at installation to activate the 10-year warranty. At a retail value of £100-£150, its inclusion is a genuine saving compared to the 600 System 2, which requires a separate filter purchase. The filter captures iron oxide and metallic debris before it reaches the heat exchanger – protecting the stainless steel component you’re paying a premium for.

The brass hydraulics block connects the heat exchanger to the central heating circuit. Brass handles the repeated thermal cycling and corrosion of daily use considerably better than the plastic or composite alternatives found in lower-tier boilers, and it’s part of why Baxi installers with 30 years of experience keep coming back to the 800 range.

The pre-heated condensate trap reduces the risk of a winter lockout from a frozen condensate pipe – a common failure point on standard traps during prolonged cold spells. The external analogue pressure gauge lets you check system pressure without opening any panels and makes self top-up straightforward enough that most homeowners can manage it without calling an engineer.

Smart control is available via the optional Baxi uSense 2 WiFi thermostat or the Baxi AmbiZen. The boiler is also OpenTherm compatible with Nest, tado, and Honeywell, and supports the IFOS weather sensor for weather compensation. For homeowners who want to push efficiency further, weather compensation adjusts flow temperature based on outdoor conditions rather than running at full output regardless of the weather outside.

Prices and installation costs

The Baxi 800 System 2 costs approximately £1,100 for the 15kW, £1,150 for the 18kW, and £1,300 for the 24kW – all including a standard horizontal side-wall flue and the Adey Micro2 filter. If a vertical roof flue is required rather than a side-wall exit, budget an additional £300-£500. For LPG properties, the conversion is software-only – no kit, no extra parts, saving £40-£60 compared to boilers that need a physical conversion kit.

Using a mid-range installation figure of £1,500:

Baxi 800 System 2 Costs
Output size	Unit cost (incl. flue + filter)	Total (incl. installation)
815 (15kW)	£1,100	£2,600
818 (18kW)	£1,150	£2,650
824 (24kW)	£1,300	£2,800

These prices assume a like-for-like system boiler replacement with an existing cylinder in place. Need a new unvented cylinder? Add £500-£1,000 plus fitting. Converting from a combi with no existing cylinder can add up to £2,000 to the total project cost.

These prices are indicative, based on our research and actual boiler prices submitted to WhatPrice by homeowners. For a full overview of Baxi pricing across the range, see our Baxi boiler prices guide. Get quotes from at least three Gas Safe registered installers, or use the WhatPrice Boiler Cost Calculator for a guide price.

Warranty and support

Ten years, parts and labour, as standard. No Baxi Assure installer tier, no conditions beyond registering the Adey Micro2 filter at installation within 30 days and servicing the boiler annually by a Gas Safe engineer.

The filter must be fitted and registered alongside the boiler. Miss the 30-day window and you risk dropping to a shorter cover period. Miss an annual service and the warranty can be invalidated. Set a reminder, or take out a service plan at installation.

💡 WhatPrice Insight: The 10-year warranty on the 800 System 2 does not require a Baxi Assure registered installer – any Gas Safe engineer qualifies. Confirm the filter has been registered before the engineer leaves on installation day.

Installation information

A like-for-like system boiler replacement on existing pipework is a one-day job. The 800 System 2’s compact dimensions and front-access design make it one of the more straightforward installs in this class. If you’re fitting a new cylinder at the same time, expect one to two days – and confirm your installer holds a G3 unvented hot water qualification alongside their Gas Safe registration.

What to expect on installation day

Do you need a system flush or filter?

The Adey MagnaClean Micro2 is included in the box and must be fitted at installation – this simultaneously satisfies the UK Building Regulations requirement for a magnetic filter on any new boiler installation and activates the 10-year warranty. No separate filter purchase needed, saving £100-£150 compared to the 600 System 2.

A powerflush of existing pipework isn’t legally required but we’d recommend it on any system over ten years old. Connecting a new boiler to pipework carrying years of accumulated sludge undermines performance from day one. Budget £350-£800 depending on the number of radiators.

Finding a Gas Safe registered engineer

All gas boiler installations must be carried out by a Gas Safe registered engineer. For a new unvented cylinder, your installer also needs a G3 qualification – confirm this at the quoting stage. Use the WhatPrice quote service to be matched with vetted, Gas Safe registered installers in your area.

Reviews and ratings

Baxi holds a 4.6 out of 5 rating on Trustpilot UK, based on over 76,000 reviews.

Positive reviews

Engineer quality is the standout theme, and it comes up repeatedly in the 800 pool. Owners describe engineers arriving on time, diagnosing faults quickly, and carrying the right parts in the van – including heat exchangers, PCBs, igniters, and diverter valves replaced in a single visit under warranty. One owner had a PCB failure on Christmas Eve and an engineer on-site by Boxing Day morning.

An 800 System owner who replaced an older Ideal boiler reports it is quicker to heat up, quieter, and cheaper to run within two years. An installer with 30 years of Baxi experience – who has fitted the Bermudas, 105, Platinum, and Duo-tecs – singles out the 800 Mk2 as the model he fits most now, citing reliability and Baxi’s service and back-up as the reason he hasn’t switched manufacturer.

The 10-year warranty earns specific mentions as a deciding factor at the point of purchase. Several owners describe booking an engineer, having the fault resolved under warranty with no charge, and coming away more confident in the product than they went in – which is the warranty doing exactly what it’s supposed to do.

Negative reviews

One review noted a persistent heat exchanger blocking issue in one household – a new build installation with all-new plastic pipework that has suffered repeated exchanger blockages over roughly a year despite following every Baxi engineer advisory, including system draining, inhibitor treatment, magnetic filter installation, and limescale filter fitting. Baxi’s response attributes the problem to water quality. The case is an outlier in the review pool but it’s a detailed account and worth reading in full if you’re in a hard water area and considering the 800 System.

How the Baxi 800 System 2 compares

Baxi 800 System 2 Comparison Table
Model	Baxi 800 System 2	Baxi 600 System 2	Worcester Bosch Greenstar 4000 System
Typical unit price (18kW)	£1,150	£1,250	£1,250
Heat exchanger	Stainless steel	Stainless steel	Aluminium
Standard warranty	10 years	7 years	5 years
Max warranty	10 years	7 years	10 years
Filter included	Yes (Adey Micro2)	No	No
Built-in WiFi	No	No	Yes
App control	uSense 2 (optional)	uSense 2 (optional)	EasyControl (built-in)
LPG compatible	Yes (no kit)	Yes (no kit)	Yes
Max output	24kW	24kW	24kW

For personalised guidance on choosing the right boiler, we recommend speaking with a Gas Safe registered engineer.

Final thoughts – is the Baxi 800 System 2 right for you?

If you’ve been reading the 600 System 2 guide alongside this one, the decision comes down to how long you plan to own the boiler. The 800 System 2 costs around £100 more at the 18kW but adds three years to the standard warranty (10 vs 7) and includes the Adey filter that the 600 requires you to buy separately. Net the filter saving against the price premium and the real difference is closer to £50 for an extra three years of parts and labour cover. For most homeowners, that’s an easy call.

Against the Worcester Bosch Greenstar 4000 System, the 800 System 2 is similarly priced at the 18kW, carries a longer standard warranty (10 years vs 5), includes the filter, and brings a stainless steel heat exchanger against Worcester’s aluminium. Worcester counters with built-in WiFi and a 1:10 modulation ratio – genuinely useful features if smart connectivity from day one is a priority. For homeowners who want the better heat exchanger material, the longer accessible warranty, and the included filter without navigating installer tiers, the 800 System 2 is the stronger package.

The noise concern in the review pool is worth factoring in if the boiler position is adjacent to a bedroom or living space. It’s a minority complaint but specific enough to raise with your installer before committing – particularly for loft installations where the sound has more routes through the structure to reach living areas.

FAQ