Baxi 836 Review: Specs, Warranty and Faults

Is the Baxi 836 any good?

For a busy home with a bathroom and an ensuite, yes. The 836 is the top model in Baxi's 800 Combi 2 range, and it is the range Baxi puts its longest warranty on. It arrives with a magnetic system filter in the box, and it delivers the strongest hot water flow of the three models, which is the whole reason to buy it.

What is genuinely good about it

• 15 litres a minute of hot water at a 35°C rise, the highest in the 800 Combi 2 range and enough to keep a shower usable while a tap is running.
• A 10-year parts and labour warranty, the longest Baxi puts on any of its boilers.
• An Adey Magnaclean Micro 2 system filter supplied with the boiler, so the sludge protection is not sold to you as an extra.
• An Easy-Fill permanent filling link, so topping up the pressure does not mean hunting for a filling loop under the boiler.
• Compatible with Baxi's uSense smart control and with OpenTherm controls, which let the boiler modulate down instead of firing flat out and switching off.
• The same 700mm by 285mm casing as the smaller models, so the extra hot water does not cost you cupboard space.

What is honestly less good

• "836" is the hot water number, not the heating number. Central heating output is 25kW maximum, so the extra money buys hot water, not a warmer house.
• A combi can only deliver what your cold mains brings into the house. If your incoming flow and pressure are weak, the 836 will not fix that, and a stored hot water system will serve you better.
• The 10-year warranty has four conditions attached, and one of them, keeping the supplied filter fitted and maintained, is easy to forget years later.
• Its minimum heating output is 7.2kW, higher than the smaller models. In a small, well insulated home an oversized combi cycles on and off, which is not how you get the efficiency you paid for.

Is the Baxi 836 the right size for your home?

The 836 is the high hot water demand model. Baxi's own data for the 800 Combi 2 range sets the three models side by side, and almost every difference is about hot water rather than heat.

Read the heating row before you spend the extra. The 836 heats your radiators no harder than an 830 does. What the extra money buys is close to three more litres of hot water a minute, which is the difference between one shower working well and a shower and a tap working at the same time.

Flow rate is the number you actually notice. Baxi's own figures put the 836 at 15.0 litres a minute, against 12.2 for the 830 and 10.2 for the 824, so the 836 gives you close to three more litres a minute than the model most people compare it with. That is why the 836 suits a family home with a bathroom and an ensuite, and why an 830 is usually enough where there is one bathroom.

Two warnings. First, none of this replaces a heat loss calculation done in your house by a Gas Safe registered installer: a bedroom count is a rule of thumb, not a sizing method. Second, if your home is larger again, or two showers genuinely run at once, a combi is the wrong shape of appliance and a heat only or system boiler with a hot water cylinder will serve you better. The Baxi 830 review covers the model most people compare this one against.

Where can the Baxi 836 be installed?

In most of the usual places: a kitchen, a utility room, an airing cupboard, or a loft with the proper protection. Baxi gives the 800 Combi 2 casing as 700mm high, 395mm wide and 285mm deep, with an installer lift weight of 30.5kg for the 836. It fits inside a standard kitchen wall unit.

What decides the job is the space around the boiler, not the box itself. Baxi's installation manual for the range asks for clearance above, below and at each side, and 450mm in front of the boiler for servicing. That front clearance is the one that catches people out, because a cupboard door and a wall opposite can turn a technically legal position into one an engineer cannot work in.

The other decider is the flue. Where the flue terminal can safely come out of the wall, and whether the existing hole still complies, is usually what makes a straight swap simple or awkward. Only the installer can judge that on site, so treat any quote given over the phone without a survey as a rough number.

How efficient is the Baxi 836?

Baxi's technical data for the 800 Combi 2 gives the range an A for water heating efficiency. Baxi does not publish a seasonal space heating efficiency percentage or an ErP heating class for the range on its current product page, so if you need those figures for a grant or a quote, ask your installer for the energy label supplied with the boiler.

Any efficiency rating is measured on a test rig, not in your house, and the way you run the boiler moves the real figure more than the badge does. A condensing boiler only condenses, and only reaches its best efficiency, when the water coming back from the radiators is cool enough. Turn the heating flow temperature down, let the boiler run long and gentle rather than short and hot, and you get closer to the number on the label.

This is also why the OpenTherm and uSense compatibility is worth using rather than ignoring. A modulating control holds the 836 near its 7.2kW minimum instead of firing it at 25kW and switching it off again, and short cycling is where efficiency quietly disappears.

The 10-year warranty, and what cancels it

Baxi gives the 800 range a 10-year parts and labour warranty. It is a real warranty, and it is conditional. Baxi's published conditions are that the boiler is:

1. registered within 30 days of installation, by either the installer or you,
2. installed with the Benchmark checklist completed by the installer,
3. serviced every year, and,
4. on the 800 range specifically, fitted with the supplied magnetic filter, maintained for the length of the warranty.

Miss the filter condition and Baxi says the warranty reverts to two years. Miss the registration, the Benchmark checklist or the annual service and Baxi says the warranty reverts to the standard one year. Register it inside the 30 days and keep every service certificate.

Baxi is also explicit that parts damaged by sludge and dirt in the system water are not covered, which is exactly why the filter condition exists. When you book the annual service, ask the engineer to clean the filter at the same visit and to write both jobs on the paperwork.

Baxi's own warranty information page carries the current terms. Our Baxi warranty guide explains how registration works, how to check what you have left, and what to do if you inherited a boiler with no paperwork.

Key features

Easy-Fill filling link

The 836 has a permanent filling link built in, worked by a single spring-loaded lever. It lets you put the central heating pressure back up yourself without hunting for a braided filling loop, and it is one of the few maintenance jobs on a modern combi a homeowner can safely do. Follow the steps in the Baxi user guide that came with the boiler.

One caveat worth knowing: a boiler that needs topping up more than once or twice a year is losing water somewhere, and repeated topping up hides the leak rather than fixing it. Our guide to a boiler that keeps losing pressure explains what an engineer looks for.

Magnetic system filter included

The 836 is supplied with an Adey Magnaclean Micro 2 filter. It is a compact magnetic filter that catches the iron oxide particles circulating in the system water and holds them away from the boiler. Left alone, those particles become sludge, which causes cold spots at the bottom of radiators, poor circulation, and eventually a failed pump or heat exchanger. On this boiler the filter is not optional: it is one of the four warranty conditions.

Smart and modulating controls

The 836 works with Baxi's uSense Wi-Fi thermostat, which lets you set the heating schedule and change it from your phone while you are out. It also works with OpenTherm controls, which is the more useful of the two for running costs. An OpenTherm thermostat measures how far the room is from the temperature you asked for and tells the boiler to burn only as hard as it needs to, instead of the blunt on and off switching of a basic thermostat.

Simple digital display

The front panel is an LCD display, showing the system pressure and any fault code. If a code appears, write it down before you do anything else. It is the single most useful piece of information you can give an engineer on the phone.

What goes wrong with a Baxi 836?

Nothing unusual, and most call-outs on a boiler like this are caused by the system around it rather than the appliance. The 836 shows an E code when it locks out. Codes you may see include E118 for low system pressure, E128 for a flame failure while running, E133 for an ignition failure, and E125 for a circulation fault on the heating side.

The safe homeowner step is the same for all of them: reset the boiler once. If the code comes straight back, book a Gas Safe registered engineer rather than sitting there resetting it. Where the code points to a gas supply or ignition problem, such as E133, do not keep resetting it at all, and if you smell gas call the National Gas Emergency Service on 0800 111 999. Our Baxi fault code list goes through the codes in more detail.

Where to stop. Checking the pressure gauge, checking the gas is on elsewhere in the house, and pressing reset once are homeowner jobs. Opening the case is not. Only a Gas Safe registered engineer may work on the gas side of a boiler. If you smell gas, do not touch the boiler and do not use light switches: leave the property and call the National Gas Emergency Service on 0800 111 999 straight away.

Baxi 836 specifications

Figures are taken from Baxi's own technical data for the 800 Combi 2 and from its warranty pages. Baxi has revised this range more than once, so check the data badge on your own boiler before ordering parts or a flue.

Need more help with your Baxi boiler?

If something is actually wrong, tell us what the boiler is doing and we can arrange a Gas Safe registered engineer. If you are choosing between an 830 and an 836, we can put you in front of an installer instead. Either way, ask for a free callback and someone will call you back.

Once the Baxi warranty ends, or if its conditions were never met, repairs are yours to pay for per visit. That is the point where a boiler and central heating cover plan starts to earn its keep. Smart Plan is a service plan rather than insurance, you pick only the modules you want, and we work with a national network of thousands of Gas Safe registered engineers. The plan runs monthly, and once you use a service a 12-month agreement period applies. We aim to get an engineer out to you within two working days, and cover plan call-outs are booked Monday to Friday, 08:00 to 18:00. A £95 call-out fee applies in some situations, including during the first 30 days of a plan, when your cover still applies. Boiler and central heating repairs are covered up to £500 in a 12-month period if the boiler is under seven years old, or £200 if it is over seven years old.