Baxi E133 Fault Code: Boiler Failed to Light

What does E133 mean on a Baxi boiler?

E133 appears on Duo-tec, Platinum, EcoBlue and the 600 and 800 series, and it is a lockout rather than a warning. The board asked for a flame, ran the full ignition sequence, waited for the flame sensing electrode to report a flame current back, and got nothing. Baxi allow a set number of attempts before the board gives up and holds the boiler off. That is why E133 does not clear on its own and needs a deliberate reset from the front panel.

It is worth being clear about what the lockout is. The boiler has not broken by displaying E133. It could not establish a flame safely, so it closed the gas valve, which is exactly what you want from an appliance with gas going into it. The job is to find out why the flame never arrived.

E133 is only the Baxi number for it. Every make has its own code for the same event, and an Ideal boiler L2 is telling you exactly what E133 does in different words. A Vaillant says it with a different number again. The list of causes behind all of them overlaps almost completely, so if the boiler in front of you is not a Baxi, the checks further down this page still apply.

What the boiler is doing when it locks out

Stand next to it and run a hot tap and the whole sequence plays out in about fifteen seconds. The fan spins up to purge the heat exchanger and prove the flue is clear, the igniter then starts, a fast tick tick tick as the electrode arcs across its gap, and at the same moment the gas valve should open.

On a healthy boiler the clicking stops after two or three seconds, because the flame has lit and the sensing electrode has told the board to stop sparking. On a Baxi heading for E133 the clicking runs its full window, stops, the fan winds down, and the whole thing repeats. After the last attempt the display shows E133 and stays there.

What you can hear narrows it down before anybody takes a cover off. Clicking with no soft woof behind it usually means no gas is arriving at the burner. A woof that catches and then dies means gas arrived but the flame was not held or not detected. No clicking at all points at the igniter, its lead or the board rather than the gas side.

One thing worth ruling out first. If the display is clear, the boiler fires normally for the radiators and only the hot water is missing, then what you have is no hot water but the heating works, and that is not an ignition lockout at all. E133 is not what you are dealing with and the fault sits somewhere else entirely. No hot water from a combi boiler while the radiators still warm up is a separate trail, and starting there will save you resetting a boiler that has nothing wrong with its ignition.

Causes of a Baxi E133, most likely first

This is roughly the order an engineer works through, most common at the top. A good share of E133 calls never get past the first three.

• No gas reaching the appliance. A prepayment meter out of credit, a supply interruption, or the emergency control valve at the meter left part closed after other work. It costs nothing to rule out and it is the single most common cause.
• A closed gas isolation valve under the boiler. Every Baxi has a small lever valve on the gas pipe entering the case, and anyone who has worked in that kitchen may have closed it and not reopened it fully.
• A frozen or blocked condensate pipe. Common in London flats and conversions where the condensate runs out through a wall in narrow plastic pipe. The trap inside the case can also silt up over the years and produce the same effect in any weather.
• Air in the gas supply after meter work. The boiler will often light on the second or third reset once the air has purged, then behave normally.
• A dirty, worn or cracked ignition electrode. Carbon builds up on the tip, the gap drifts out of tolerance, or the ceramic insulator cracks and the spark tracks to earth instead of jumping the gap. The clicking sounds perfectly normal while this happens.
• A failed flame sensing electrode or a damaged sensing lead. Gas is burning properly, but the flame current never reaches the board, so it concludes there is no flame and locks out. You can sometimes see a brief flame through the sight glass on these.
• Low gas working pressure at the appliance. Undersized or partly blocked pipework, or a shared run feeding a cooker and a boiler at once, can drop the pressure under load below what the burner needs to establish a flame.
• A faulty gas valve, and last of all a control board fault. Both are less common than people assume, and neither should be fitted until the supply and the ignition side have been proved.

How to reset a Baxi showing E133, and what to check first

None of the following involves taking a cover off, and all of it is worth doing before you call anyone out. A fair number of E133 calls are settled on the phone by one of these, and where there is no code on the display at all and simply no hot water in the property, the no hot water checklist before you call covers that same ground from the other direction.

If every one of those checks out and E133 comes back again, the fault is inside the appliance. Stop resetting at that point. Each reset drives another full ignition cycle through an electrode that is already struggling, and boilers reset twenty times in an evening tend to end up a larger repair than they started as.

• Try a gas hob. If the hob will not light either, the problem is the supply and not the boiler at all. Check the meter for credit, and check the handle on the emergency control valve at the meter is in line with the pipe.
• Find the lever valve on the gas pipe going into the underside of the boiler. In line with the pipe is open, across it is closed.
• In cold weather, follow the white plastic condensate pipe. Any section running outside can ice up overnight, usually at a bend or where it meets a drain. Feel along it for a cold solid stretch and pour warm, not boiling, water over that part to thaw it.
• Glance at the pressure gauge while you are there. A Baxi with no water in it will not fire, and that shows a different code, but it takes a second to check.
• Press and hold the reset button for the few seconds the manual specifies, and give it two attempts rather than ten. Some Baxi models limit how many resets they accept in a short period before requiring a longer wait.

If you can smell gas at any point, do not reset the boiler and do not touch any electrical switch. Turn the gas off at the meter, open the windows, and call the national gas emergency service on 0800 111 999 before you call a plumber.

How is a Baxi E133 diagnosed and repaired?

Everything behind the case is gas work and is restricted by law to an engineer qualified for it. Our engineers are qualified for the work described here. An E133 that keeps coming back is booked as a boiler diagnosis rather than as a parts swap, because the whole point of the visit is to prove which link in the chain has failed before anything is fitted.

The visit runs in a set order so the fault is proved rather than guessed at. Gas working pressure is measured at the appliance test point with a manometer, standing and then under full load, because a supply can read perfectly at rest and collapse the moment the burner calls for gas. The ignition electrode comes out and is checked for carbon, a cracked insulator and the correct gap, and the spark is watched. The condensate trap is drained and checked for silt, since a blocked trap is common on Baxi appliances that have never been serviced.

Where a flame does establish for a moment, the flame current is measured in microamps to see whether the board is genuinely being told a flame is present. Only then does attention move to the gas valve and the board. Fitting an electrode because E133 is on the display, without measuring anything first, is how people end up paying for three parts and still having the fault.

The rate is fixed before we attend and the total depends on how long the job takes. What an E133 costs therefore depends almost entirely on whether it turns out to be a closed valve or a gas valve.

When repeated E133 lockouts mean the boiler is finished

One E133 on a boiler that is otherwise sound is a repair, and often a very small one. E133 two or three times a week on an appliance well past fifteen years old that has already had a gas valve or a board is a different conversation. Parts availability is the practical limit on older Baxi models, and there comes a point where the next part costs more than it buys back. A straight engineer will tell you which of the two you are in before you spend anything.

While that is being decided there is often a stopgap in the property. Where the system has a cylinder with an immersion heater, switching it on gives you a tank of hot water on electricity while the boiler fault is sorted. It is worth checking that it genuinely heats rather than assuming, because an immersion that failed quietly months ago is normally discovered on the evening it is needed, and an immersion heater repair is a separate job from the E133 rather than a fix for it. In a block served by a thermal store instead of a boiler there is no E133 to read at all, and the appliance in the cupboard is a different machine with a different failure list.