Baxi Boiler Fault Codes Explained: E133, E119 and E110 (London Guide 2026)
Baxi or Potterton showing E133, E119 or E110? What each code actually means, the checks you can safely do yourself in five minutes, and the exact point where you must stop and call a Gas Safe engineer.
E133 is the code you are most likely to be looking up. It means the boiler ran its ignition sequence and no flame was established, or a flame it did establish was lost, so it locked out. Baxi describe it as a gas supply failure or flame lockout, and it is the one Baxi code with a decent chance of a homeowner fix: check the gas is on at the meter, check another gas appliance such as the hob still lights, check a prepayment meter is in credit, and in cold weather check the external white condensate pipe has not frozen. E119 is low water pressure, and it is the code most homeowners clear alone by topping the system up to around 1.2 bar through the filling loop. E110 is an overheat safety shutdown and it is Gas Safe engineer work every time, with no homeowner check at all. Do not reset more than two or three times. Never remove the boiler casing, and if you smell gas, stop and ring the National Gas Emergency Service on 0800 111 999 first.
A Baxi that has stopped working and is showing a code on its display has already done you a favour. It has told you which of its internal safety checks failed. The problem is that Baxi's codes are written for engineers, so E133, E119 and E110 mean very little to a homeowner standing in a cold kitchen at seven in the morning wondering whether this is a five-minute fix or a call-out.
This guide translates the codes we attend most often on London Baxi and Potterton installations. For each one you get what the boiler is actually complaining about, the checks you can safely do yourself from outside the casing, and the clear point at which you stop and ring a Gas Safe registered engineer. Nothing in here asks you to open the boiler, touch a gas component or defeat a safety device, because none of that is legal or safe for anyone who is not on the Gas Safe Register. If you are not sure your boiler is a Baxi, or you want the general principle first, start with our guide to boiler fault codes across every brand.
⚠️ Before anything else: if you can smell gas, this is not a boiler repair problem. Turn the gas off at the meter's emergency control valve, open windows and doors, do not touch electrical switches, do not use naked flames, and ring the National Gas Emergency Service on 0800 111 999. It is free and staffed 24 hours. Repairs to the appliance happen after the supply has been made safe.
How Baxi Fault Codes Work
Baxi uses an E prefix followed by a three-digit number. Depending on the model and the display, the same fault appears as E133, as E 133, or as the letter and the number alternating on a two-character display, so treat all three as identical. Some models also show the number alone.
Two things about Baxi are worth knowing before you look up a single code.
- Baxi and Potterton are the same manufacturer. They share control platforms across much of the range, so a Potterton Promax or Potterton Gold will normally display the same E-prefixed codes as the equivalent Baxi. If you have a Potterton and you have landed on a Baxi page, you are usually in the right place.
- Older Baxi units may not show codes at all. Baxi has produced a lot of ranges over the years, and the older Solo and Combi units in particular signal faults with a pattern of flashing neon lamps on the front panel rather than a numeric display. If your boiler has lights rather than a screen, a code table is not going to help you and the lamp pattern in your model's user guide is what you need.
The critical thing to understand is that a fault code names the check that failed, not the part that broke. E133 does not mean "your gas valve is dead". It means the boiler expected to see a flame and did not. That could be the gas supply, the ignition electrodes, the flame sensing electrode, the gas valve, or a blocked condensate route stopping the boiler completing its sequence. Which of them it is takes a meter and a set of eyes inside the casing, which is why for two of the three codes below the honest answer is that the diagnosis itself is engineer work.
💡 Write the code down before you reset. Some Baxi models clear the code from the display once the fault resets, and an engineer who knows you had E133 three times overnight will arrive with the right parts on the van. It is the single cheapest thing you can do to shorten a call-out. Note the model name from the front panel while you are there.
E133: Gas Supply Failure or Flame Lockout
What the boiler is saying: I ran my ignition sequence and no flame was established, or a flame I did establish went out and would not re-light, so I have locked out rather than keep trying.
E133 is the Baxi code we attend most often in London, and you can usually hear it happening: a run of clicks from the ignition electrodes, a pause, another attempt, and then the code on the display. Baxi describe it as a gas supply failure or flame lockout, and that phrasing is a genuine hint about where to look first. Because the complaint is that the boiler could not light or could not stay alight, every productive check is about whether gas is actually reaching the appliance and whether the combustion and condensate paths are clear. All of those checks sit outside the casing, and in a London winter there is a genuinely good chance one of them fixes it without a call-out at all.
What you can safely check and do yourself
Confirm the gas supply is actually on
Find the emergency control valve at the gas meter. When the lever sits in line with the pipe the gas is on; across the pipe it is off. It is more common than you would think for a valve to have been turned off during other work and never turned back.
Test another gas appliance
Try the gas hob. If the hob will not light either, the problem is the supply rather than the boiler, and that is a very different phone call. If the hob lights normally, gas is reaching the property and the issue is at the boiler.
Check the meter is in credit
On a prepayment meter, a boiler that has run out of credit and been topped back up sometimes needs the emergency credit accepted at the meter before gas flows properly again. Worth 30 seconds before you pay a call-out fee.
In cold weather, check the condensate pipe
Find the white plastic pipe leaving the property, usually 22mm or 32mm and often the only white pipe on that wall. After a hard frost it can freeze solid, and a blocked condensate route is a very common cause of a January lockout in London, frequently accompanied by a gurgling sound as the boiler tries and fails. Pour warm, never boiling water along it, concentrating on external bends and the exposed end. Boiling water can crack the pipe or its fittings.
Reset once, and once more at most
Hold the reset button until the display shows the boiler restarting. If it fires and stays running, you have found it. If E133 returns, stop resetting and book an engineer.
When you stop and call an engineer
If the gas is on, other appliances work, the meter is in credit and the condensate pipe is clear, then the remaining causes all sit inside the appliance. The gas valve, the ignition and flame sensing electrodes, the fan and the flue are Gas Safe territory without exception. Two resets is the limit. A lockout after failed ignition is the boiler doing precisely what it is designed to do, and repeatedly forcing it to retry a start sequence it has already judged unsafe is the one thing you should not do.
✓ If a frozen condensate pipe turns out to be the culprit and it keeps refreezing every cold snap, ask an engineer to re-route it internally or lag it properly. It is a cheap job that saves a winter of call-outs, and we cover the wider picture in our frozen pipes guide for London.
E119: Low Water Pressure
What the boiler is saying: there is not enough water in the sealed heating circuit for me to fire safely, so I have stopped before I damage the heat exchanger by running it dry.
This is the friendliest code on the page, and the only one a homeowner can usually resolve without an engineer, because everything you need to touch is outside the casing.
What you can safely check and do yourself
- Read the pressure. Most Baxi installations have an analogue gauge on or near the boiler; newer models show a digital pressure reading on the display. Below about 1 bar when the system is cold is low, and somewhere around 0.5 bar is where the boiler stops.
- Top the system up through the filling loop. On most Baxi installations this is a short braided metal hose with lever or tap valves underneath the boiler. A number of Baxi models use a built-in filling arrangement instead, so if there is no braided hose in sight, check your model's user guide rather than hunting around for one. Our step-by-step repressurising guide walks the whole process and shows the valve types you will meet on Baxi and Potterton units.
- Stop at 1.2 bar. Do it with the boiler switched off and cool, open the valve or valves slowly, and close them the instant the reading hits 1.2. Releasing excess pressure is far more awkward than adding it.
- Reset once if the code has not cleared by itself when you switch the boiler back on.
When you stop and call an engineer
Call if the pressure will not rise at all when you open the filling loop, if the code persists at 1.2 bar, or if the gauge reads above 2.5 to 3 bar, in which case the answer is to release pressure rather than add it and that is not a homeowner job.
More importantly, call if E119 keeps coming back. A sealed system that is behaving should hold pressure for six to twelve months between top-ups. If you are topping up weekly, the water is going somewhere: a weeping radiator union, a hidden pipe joint, a failed expansion vessel, or a pressure relief valve discharging out through the wall. Repeated topping up masks the fault and pumps fresh oxygenated water into the system, which accelerates corrosion in the radiators and the heat exchanger. We rank the four causes by how often we actually see them in why your boiler keeps losing pressure.
✓ Free 30-second diagnostic: step outside and look at the brass pipe that terminates low on the external wall near the boiler. If it is wet, dripping, or streaked with white limescale, the pressure relief valve has been discharging and your E119 almost certainly traces back to a failed expansion vessel. Telling the engineer that on the phone can halve the diagnosis time on site.
⚠️ If the pressure is dropping because water is visibly coming out somewhere, isolate the water before you worry about the boiler code. Our guide to turning the water off at the mains in London covers where the stopcock hides in Victorian terraces, 1930s semis and flats, and how to isolate a single radiator or appliance instead of the whole property.
E110: Overheat Safety Shutdown
What the boiler is saying: I measured a temperature above my safety limit, or my limit thermostat operated, and I shut down to protect the heat exchanger and the system.
E110 has the shortest homeowner section on this page, because there is not one. A safety limiter has operated, and that is a device doing exactly what it exists to do. Every part of the diagnosis sits inside the casing, so E110 is Gas Safe engineer work every single time.
What is useful to know is why it happens, because it is rarely the safety device itself at fault. E110 nearly always traces back to heat not being carried away from the heat exchanger fast enough. The usual chain is a pump that is failing or airlocked, a circuit restricted by magnetite sludge, closed or seized valves, or a primary heat exchanger that has scaled up. That last one is a common finding in London, where hard water across most of the north and west of the capital furs up heat exchangers faster than the national average.
What you can safely do
- Note what you observed. Were the radiators getting hot, or were some cold at the bottom? Did you hear kettling, banging or a rumbling from the boiler in the weeks beforehand? Was the pressure normal? All three help the engineer arrive with the right expectation and the right parts.
- Do not sit and reset it repeatedly. A boiler that keeps overheating and locking out is not a boiler to keep restarting. One reset to confirm the code is persistent is reasonable. Five is not.
- Turn the boiler off at the switched fused spur if it is making loud banging noises or you can smell scorching, and book the visit as an emergency.
⚠️ E110 is not a code to work around. There is no homeowner check, no external adjustment, and no acceptable way to bypass an overheat safety device. If a Baxi is repeatedly reaching E110, treat it as an emergency call-out rather than an inconvenience.
One thing worth knowing before the engineer arrives: if the diagnosis lands on sludge rather than a failed part, the real fix is a system clean and a magnetic filter, not a component swap. Replacing a pump in a system full of magnetite buys you a year at best, and our signs your radiators need a power flush guide covers the corroborating evidence you can check yourself.
Other Common Baxi Codes You Might See
A short reference for codes that turn up alongside the three above on Duo-tec, Platinum, EcoBlue and the 600 and 800 series, plus their Potterton equivalents. The right-hand column is the honest answer about who can act on it.
| Code | What it indicates | Homeowner or engineer? |
|---|---|---|
| E119 | Low water pressure in the sealed system | Homeowner can top up to around 1.2 bar via the filling loop |
| E133 | Gas supply failure or flame lockout, no flame established or flame lost | Gas, meter and condensate checks only, then engineer |
| E110 | Overheat safety shutdown | Engineer only |
| E125 | Reported on several ranges as a circulation fault, meaning the boiler did not detect the water movement it expected | Check pressure only, then engineer |
| E128 | Reported on several ranges as loss of flame while the boiler was already running | Same external checks as E133, then engineer |
| E160 | Reported on several ranges as a fan fault | Engineer only |
| E168 | A general boiler fault on a number of Baxi and Potterton models. Where it relates to condensate drainage, a frozen or blocked external condensate pipe is the first thing to rule out in cold weather | Condensate check only, then engineer, and check your model's manual for the exact meaning |
| Flashing neon lamps rather than a code | Older Baxi and Potterton units signal faults with lamp patterns, not numbers | Read the lamp pattern against your model's user guide, then ring |
| Any code you cannot find | Unknown. Baxi ranges use overlapping but not identical code sets | Note it exactly with the model name, and quote both on the phone |
We have deliberately kept that table short rather than reproducing a long list of half-remembered codes. Baxi has produced a great many ranges, and the same three digits do not always mean precisely the same thing on every one of them. Baxi publish the full fault list in the installation and servicing instructions for each specific model, and a good engineer will cross-reference your unit rather than work from a generic internet table. That is why the genuinely useful thing you can do is write down the code exactly as displayed, the model name from the front panel, and the GC number from the data badge.
Resetting a Baxi Safely
On most current Baxi and Potterton models the reset is a dedicated button on the control panel, held for a few seconds until the display shows the boiler restarting. On some models it is combined with the mode or function control, and the user guide for your unit shows which. That much is straightforward. The discipline is in how often you use it.
- Only reset after you have changed something. Topping the pressure up, thawing a condensate pipe or turning the gas back on are changes. Pressing reset again five minutes later is not.
- Two or three attempts, maximum. Once a fault persists through a small number of resets, stop and get qualified help.
- A code that clears and returns the same day is a persistent fault. Book the visit rather than resetting through the evening.
- Never reset an overheat code repeatedly. E110 is the one code where even a second or third attempt is questionable.
The lockout is not the boiler being awkward. It is a safety mechanism that has decided a start sequence is not safe to repeat, and overriding it by habit is how a cheap sensor fault becomes an expensive one.
Where You Must Stop: The Gas Safe Line
This is the part that matters more than any code on this page. Under the Gas Safety (Installation and Use) Regulations 1998, work on a gas appliance in the UK may only be carried out by an engineer on the Gas Safe Register. Removing the casing of a sealed-system gas boiler counts as work on the appliance. It is a criminal offence for anyone else to do it, it invalidates the boiler warranty and often the home insurance, and it puts you alongside live mains electrics, a pressurised water circuit and a gas carrying component simultaneously. It also breaks the room-sealed integrity of the appliance, which is what keeps combustion products in the flue rather than in your home.
So the boundary is simple and it is physical: outside the casing is yours, inside the casing is not.
💡 Outside the casing, and yours to do: reading the pressure gauge or digital pressure display, using the external filling loop, checking the gas meter's emergency control valve and other gas appliances, confirming prepayment credit, thawing an external condensate pipe with warm water, checking the outside pressure relief discharge pipe for drips, checking the room thermostat and radiator valves, using the reset control, and writing the fault code down.
⚠️ Inside the casing, and never yours to do: the pump, the gas valve, the ignition and flame sensing electrodes, the fan, the overheat limiter, the expansion vessel, the pressure relief valve, the diverter valve, the heat exchanger, the PCB and the flue. There is no exception to this for "just having a look", and there is no circumstance in which bypassing or defeating a safety device is acceptable.
When an engineer does attend, ask to see their Gas Safe ID card and check the registration number at gassaferegister.co.uk. The card shows which appliance types they are qualified to work on, and the number on the card should match the one on your invoice.
What These Repairs Typically Cost in London (2026)
Indicative London pricing. The call-out covers travel and the first 45 minutes on site including diagnosis, and any parts are quoted before fitting rather than after.
| Job | Typical London cost (2026) | Notes |
|---|---|---|
| Call-out + diagnosis (weekday daytime) | £60 | Includes first 45 minutes on site |
| Call-out + diagnosis (out-of-hours / weekend) | £90 | Same 45-minute window |
| Repressurise, reset or minor fix (no parts) | £60–£120 | Often completed inside the call-out window |
| Frozen condensate re-route + lag | £90–£160 | Stops the E133 recurring every cold snap |
| Expansion vessel / pressure relief valve | £120–£280 | The usual cause behind a repeating E119 |
| Diverter valve replacement | £150–£320 | Common combi hot-water fault |
| Pump replacement | £180–£380 | Part and labour, one of the circulation-fault outcomes |
| Fan replacement | £200–£420 | Part price varies by model |
| PCB (circuit board) replacement | £350–£650 | Often the repair versus replace tipping point |
| Primary heat exchanger | £450–£750+ | Scale-related, and a frequent E110 outcome; may favour replacement |
Two things are worth knowing before you book. First, the call-out is not dead money: on most fault code jobs the diagnosis and a minor fix both happen inside that first window, so plenty of visits finish at the £60 to £120 mark. Second, if the diagnosis lands on a PCB or a heat exchanger on a boiler that is already 12 to 15 years old, pause and price a replacement before committing. Our emergency boiler repair guide for London sets out the full repair versus replace maths.
Landlords: A Fault Code Is a Repair Clock Starting
If you let the property, a locked-out boiler is a legal matter as well as a practical one. Under Section 11 of the Landlord and Tenant Act 1985 you must keep the installations for space heating and hot water in repair and proper working order. Under the Homes (Fitness for Human Habitation) Act 2018, a home left without heating or hot water, particularly in winter or where a child, an elderly or a vulnerable tenant lives, can be judged unfit for human habitation.
There is no single statutory deadline, but the accepted benchmark is to act within roughly 24 hours for a total loss of heating or hot water, and same day where a vulnerable person is affected. Two practical points: ask the tenant to photograph the display showing the code, which speeds up the dispatch and gives you a dated record, and never coach a tenant into opening the boiler. Separately, the annual Gas Safety Record (CP12) from a Gas Safe engineer is required for every gas appliance in the property regardless of whether anything has broken.
Frequently Asked Questions
What does E133 mean on a Baxi boiler?
How do I fix E133 on a Baxi boiler myself?
What does E119 mean on a Baxi boiler and can I fix it myself?
What does E110 mean on a Baxi boiler?
Are Baxi and Potterton fault codes the same?
How many times can I reset a Baxi boiler?
Is a Baxi fault code an emergency?
Can I take the cover off my Baxi boiler to look inside?
The Bottom Line
Of the three codes, E119 is the only reliable homeowner fix, and even then a repeating E119 is a leak or an expansion vessel telling you something. E133 is the one worth your time on a cold morning: four checks (gas on, other appliances, meter credit, frozen condensate) and a decent chance of clearing it yourself in a London winter. E110 gives you none, because an overheat limiter is a safety-critical device in a sealed combustion system and there is no homeowner version of that job. Past those points, the code stops being information you can act on and becomes information your engineer needs.
Note the code exactly as displayed along with your model name, do the outside-the-casing checks, reset no more than twice, and if you smell gas ring 0800 111 999 before anything else.
Emergency Repairs London provides same-day and 24/7 emergency boiler repair with Gas Safe registered engineers across all 32 London boroughs, including Baxi and Potterton diagnostics and fan, pump, gas valve and expansion vessel replacement. Fixed £60 daytime call-out, quoted before work starts. Lines are open 24/7 on 0207 046 1363.
Key Takeaways
- Baxi and Potterton are the same manufacturer and share control platforms, so a Potterton Promax or Gold will normally show the same E-prefixed codes as the equivalent Baxi.
- E133 is a flame or gas supply lockout: the boiler tried to light and no flame was established, or a flame was lost. It is the most common Baxi code we attend in London.
- E119 is low water pressure. Top the system up to around 1.2 bar through the filling loop. This is the one code most homeowners fix without an engineer.
- E110 is an overheat safety shutdown. There is no homeowner check, no external adjustment and no safe workaround. It is engineer work every time.
- A frozen external condensate pipe is a very common cause of a January E133 in London, and thawing it with warm water is a legitimate homeowner fix.
- Do not press reset more than two or three times, and only after you have actually changed something. Repeated resets on an unresolved gas fault are exactly what the lockout exists to prevent.
- Never remove the boiler casing. Under the Gas Safety (Installation and Use) Regulations 1998 that work is restricted to a Gas Safe registered engineer, and it is a criminal offence otherwise.
- Any smell of gas is not a boiler repair call. Turn the gas off at the meter, ventilate, and ring the National Gas Emergency Service on 0800 111 999.
- A London Gas Safe call-out is £60 weekday daytime and £90 out-of-hours, covering travel and the first 45 minutes including diagnosis.
