Baxi 800 Combi Problems — Fault Codes & Fixes
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The Baxi 800 is a solid mid-range combi boiler found in thousands of UK homes, and like any heating system, it can develop faults over time. Most problems — whether low pressure, ignition failures, or hot water issues — follow predictable patterns that you can often diagnose yourself before calling an engineer. This guide walks you through the most common fault codes on the Baxi 800, what they mean in plain English, and which fixes are safe to attempt at home versus which ones require a Gas Safe registered engineer. Understanding your boiler's language takes the mystery out of breakdowns and can save you time and money, especially if your system is still under warranty.
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Most likely cause & what to check
The Baxi 800 is a step up from the budget 600 range — it is a mid-range combi boiler with a cleaner design, better controls, and a longer warranty. It shares the same fault code system as the 600 but has more robust components. Manuals and fault guides at baxi.co.uk/support or 0344 871 1525.
Fault code E119 (low pressure): repressurise using the filling loop to 1.2 bar and press reset. The Baxi 800's filling loop is located under the boiler and has clearly labelled valves.
Fault code E133 (ignition failure): reset once. Check gas supply. If E133 returns, call a Gas Safe engineer — ignition components on the 800 are straightforward to access and replace.
Fault code E168 (fan fault): as with all gas boilers, a fan fault must be investigated by a Gas Safe engineer. Do not continue resetting.
No hot water but heating working (or vice versa): this points to a diverter valve fault. Less common on the 800 than on some other ranges, but it does occur. A Gas Safe engineer can replace the diverter valve assembly.
The Baxi 800 typically carries a 5-year parts and labour warranty when registered within 60 days of installation. Check baxi.co.uk/warranty for your specific warranty terms.
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Frequently asked questions
What does fault code E119 mean on my Baxi 800?
E119 indicates low water pressure in the system, usually below 1 bar. This is one of the easiest faults to fix yourself — you simply need to repressurise the boiler using the filling loop (located under the unit) until the pressure gauge reads 1.2 bar, then press the reset button.
My Baxi 800 keeps showing E133 — is it dangerous?
E133 is an ignition failure code, which means the boiler cannot light the burner. A single reset is worth trying, and you should check that gas is reaching the boiler, but if the fault returns immediately, stop resetting and contact a Gas Safe engineer — repeated attempts won't fix the underlying problem and could indicate a component that needs replacing.
I have heating but no hot water — what's wrong?
This classic symptom usually points to a faulty diverter valve, the component that switches water between your radiators and your hot tap. Whilst less common on the Baxi 800 than some rivals, it does happen and requires a Gas Safe engineer to replace the valve assembly — it's not a DIY fix.
Is the Baxi 800 still covered under warranty if it develops a fault?
The Baxi 800 typically comes with a 5-year parts and labour warranty, but only if you register it with Baxi within 60 days of installation. Check your paperwork or visit baxi.co.uk/warranty to confirm your specific cover, as this will determine whether repairs are free or chargeable.