Baxi 800 Review: Specs, Sizes and Warranty

Is the Baxi 800 any good?

Yes, for most homes, and the honest reasons are boring ones. The Baxi 800 Combi 2 is compact, it is rated A for water heating efficiency across all three sizes, and Baxi puts an Adey MagnaClean Micro2 system filter in the box rather than leaving it as an upsell. That filter matters more than any brochure line, because dirty system water is what wrecks heat exchangers and pumps.

Baxi's homeowner page offers a “10-year parts and labour warranty” on the 800 Combi 2, subject to the conditions set out below. It also carries a dagger, and the small print behind that dagger is the most important thing on this page, so it has its own section below.

What is genuinely good about it

• It fits. 700mm high, 395mm wide and 285mm deep, which clears a standard kitchen cupboard.
• It is light to hang. Baxi quotes an installer lift weight of 29.2kg to 30.5kg depending on model.
• Topping up the pressure is a homeowner job. Baxi fits EasyFill, which it describes as making it “easy to top up the central heating system pressure”.
• It runs on natural gas or LPG with a manual conversion, which is useful off the gas grid.
• It is ready for hydrogen blending. Baxi's installation and service manual states the appliance “is suitable for G20 gas containing up to 20% hydrogen”.
• It has a pre-heated condensate trap, Baxi's answer to the freezing problem that stops so many condensing boilers in January.

Where it is weaker than the marketing suggests

• The 836 gives you no more heating than the 830. Baxi's own figures put maximum central heating output at 27.1kW for both. The extra you pay buys hot water flow, not radiator power.
• The flow rates are quoted at a 35°C temperature rise. Mains water arrives colder in winter than in summer, so the same boiler feels weaker in January at the same litres per minute.
• A combi cannot beat your incoming water main. If the main into the house is weak, a bigger 800 will not fix it. Ask the installer to measure flow and pressure before you choose a model.
• Servicing needs room. Baxi asks for 450mm of front clearance for servicing, so a boiler that fits the cupboard can still be awkward to work on.
• The warranty conditions are ongoing, not a one-off form signed on installation day.

Which Baxi 800 do you need?

Pick the size on hot water demand, not on how big the house feels. The number in the model name is the hot water output in kilowatts. Baxi sells the 800 Combi 2 “in outputs of 24, 30 and 36kW”.

A rough way to read that: the 824 suits a flat or a small house with one bathroom, the 830 suits a typical three bedroom house with one bathroom, and the 836 earns its money where a shower and a tap get used at the same time. That is a guide, not a survey. Only a heat loss calculation done in your house by a Gas Safe registered engineer settles the right size, and oversizing costs you money at the till rather than saving you anything later.

All three take a maximum central heating system volume of 100 litres and carry a 7 litre integral expansion vessel, so a very large radiator circuit is worth checking rather than assuming.

Baxi 800 combi, system and heat: three different boilers

Much of the confusion around this range comes from Baxi reusing the 8xx numbers. There are three separate product lines, and a quote that just says “Baxi 830” could mean two different appliances.

• 800 Combi 2 – 24, 30 and 36kW. Heats water on demand, no cylinder, no loft tanks.
• 800 System 2 – 18, 24 and 30kW. Works with a hot water cylinder on a sealed system, no loft cisterns. Same 700mm x 395mm x 285mm case as the combi.
• 800 Heat – 16, 19, 25 and 30kW. The heat only boiler, needing a cylinder. Smaller and much lighter at 625mm high, 370mm wide and 270mm deep, with a lift weight from 17.4kg.

If you are weighing a combi against a cylinder system, settle that question before you settle on a brand, because it is much harder to reverse later.

What does a Baxi 800 cost?

Baxi does not publish a price for the 800 on its own website, and that is not evasion. Baxi sells through installers and merchants, so the number that matters to you is the fitted price your installer quotes, not a list price for the appliance on its own.

What actually moves that fitted price:

• Which model you take, and whether it is the combi, system or heat only version.
• Whether the flue can reuse the existing route, or needs a new one.
• Whether the system gets a proper chemical flush, and whether the supplied filter is fitted correctly.
• Any pipework changes, the condensate run, and the size of the gas supply pipe.
• The controls needed to meet Boiler Plus, covered next.

Get two or three itemised quotes from Gas Safe registered installers, and check in writing that warranty registration is included. Two quotes for the same 830 can differ by hundreds of pounds and both be honest, because they are quoting different amounts of work. If you are still deciding whether to replace at all, price the likely repair first and compare it against the fitted quote.

Boiler Plus: the part that adds cost in England

In England a new combi cannot be fitted on its own. The government's Boiler Plus standards, in force from April 2018, set the minimum performance standard for domestic gas boilers in English homes “at 92% ErP” and make “timers and room thermostats an explicit requirement”. On top of that, when a gas combination boiler is installed one extra energy efficiency measure is required, chosen from “flue gas heat recovery systems”, “weather compensation”, “load compensation” or “smart controls featuring automation and optimisation functions”. Baxi's uSense smart control and its outdoor sensor are two ways of meeting that requirement. Whichever route your installer proposes, it should be itemised on the quote. You can read the standards in the government's own Boiler Plus factsheet.

The 10 year warranty, and what it asks of you

The headline is real: Baxi lists a 10 year parts and labour warranty on the 800 Combi 2. The conditions are where people come unstuck, and none of them are unusual, they are just easy to forget.

• Register within 30 days. Baxi's own guide is blunt: “the warranty must be registered within 30 days of installation”. Miss that window and, in Baxi's words, “the warranty will revert to the standard one year”. The same one year applies if the Benchmark checklist is not completed or an annual service is not carried out.
• The Benchmark checklist must be completed. Baxi says “your installer must complete the Benchmark checklist”. Keep it with the manual, and photograph it.
• Service it every year. Baxi requires you to arrange an annual service, during which the engineer should check that the water in the heating system is clean.
• Keep the filter. On the 800 range the supplied magnetic filter has to stay fitted and maintained for the length of the warranty, and Baxi states that otherwise “the warranty will revert to only two years”. Ask for it to be cleaned at every service.
• Dirty water is not covered. Baxi states that if “the boiler components are damaged because of sludge and dirt in the system water, this won't be covered by the warranty, and may incur a charge to repair”.

Worth understanding: a manufacturer warranty pays for a manufacturing defect. It does not pay for the annual service that keeps it valid, and it does not pay when the fault sits in the system rather than the boiler. Our Baxi warranty guide sets out what is and is not included, and explains where a warranty stops and a cover plan starts.

What goes wrong with a Baxi 800

None of this is unique to Baxi. These are the faults that bring an engineer out to a modern condensing combi of any badge.

Pressure loss and a lockout

A sealed system that keeps dropping below its normal band will lock out and stop heating. Repressurising with the EasyFill link once or twice a year is normal. More often than that means water is escaping somewhere, and topping it up again treats the symptom. Our guide to Baxi boiler pressure covers the safe homeowner steps, and error E119 is the code you are most likely to see with it.

A frozen condensate pipe in cold weather

This is the classic winter call-out, and Baxi documents it directly: “If your boiler has shut down and is showing error code E28, E53, E133, E119 or E128 then your condensate pipe may be frozen.” Baxi's own instruction is to switch the boiler off and turn off the electricity at the wall, find the exposed section of pipe, and warm it with a hot water bottle, a microwaveable heat pack or warm water from a watering can, explicitly not boiling water from the kettle, then restore power and restart.

Ignition lockouts and sensor faults

If the same code returns after a single reset, stop resetting. A lockout is the boiler reacting to something it has measured, and repeated resets only clear the display while the fault carries on. Note the code and the time it appeared, then book a Gas Safe registered engineer. Every Baxi code we have written up is listed on our Baxi fault codes page.

Sludge, which is the expensive one

Rust and debris circulating in the system water block heat exchangers and seize pumps, and as above, the resulting damage sits outside the warranty. Catching it is exactly what the supplied Adey filter is for, which is why leaving it uncleaned is a false economy.

Safety, and this part is not optional. Anything behind the boiler casing or on the gas circuit is work for a Gas Safe registered engineer, by law. If you smell gas or suspect a leak, do not reset anything: turn the gas off at the meter, open the windows, do not operate any electrical switches, keep naked flames away and do not smoke, then call the National Gas Emergency Service on 0800 111 999.

Baxi 800 Combi 2 specifications

Figures published by Baxi for the 800 Combi 2, with the gas data taken from Baxi's 800 Combi 2 installation and service manual. Always check the data badge on your own boiler before ordering parts.