Baxi Boiler Fault Codes Explained

Baxi fault codes at a glance

Here is the short version. The first group has a safe home fix. The rest need an engineer.

• E1, E118, E119 — low pressure. You can usually top these up yourself.
• E110 — boiler overheat. Engineer.
• E125 — poor circulation. Engineer.
• E131 — flue overheat lockout. Engineer.
• E133 — gas, ignition or a frozen condensate pipe. Thaw the pipe if it is cold out; otherwise engineer.
• E20, E28 — sensor faults. Engineer (thaw the condensate first for E28 in winter).
• E160 — fan fault. Engineer.
• E168 — PCB lockout. Try one reset; otherwise engineer.

What a Baxi fault code actually means

Modern Baxi combi, system and heat-only boilers — the 600, 800 and Platinum ranges — flash a code on the display when they lock out. The lockout is deliberate. The boiler has spotted a problem and shut itself down to stay safe.

The letter is always "E" for error. The number tells you the area: pressure, overheat, gas, fan, sensor or control board.

One thing worth knowing early. The same number can mean slightly different things across Baxi ranges. An E-code on a 600 is not guaranteed to read identically on a Platinum. Treat this page as a guide, not a diagnosis for your exact model. Your boiler manual, or the label inside the casing flap, has the definitive list for your unit.

Which faults you can fix, and which you cannot

Keep this simple. Only the low-pressure codes have a safe home fix.

If your Baxi shows E1, E118 or E119, you can top up the pressure yourself. A frozen condensate pipe in cold weather is also a safe fix — thaw the outside pipe with warm water. And you can reset a locked-out boiler once to see if the fault clears.

Everything else — overheat, circulation, gas, ignition, fan, sensor and control-board faults — is engineer only. Those involve the sealed circuit, the gas side or the electronics, and it is illegal for anyone who is not Gas Safe registered to work on them.

One rule that saves a lot of trouble: reset the boiler once. If the same code comes straight back, stop. Repeatedly clearing a code overrides a safety device and can turn a small fault into an expensive one.

Low pressure faults — E1, E118 and E119

Low pressure is far and away the most common reason a Baxi locks out. The boiler needs the water in the system to sit at roughly 1 to 1.5 bar when cold. Drop below about 0.5 bar and it shuts down.

The Baxi E1 boiler fault is the classic low-pressure lockout, and you will see it on older Baxi, Potterton and Main units. The Baxi E118 fault is the same story on other models — system water pressure has fallen below the safe minimum. And the Baxi E119 fault points to the water pressure switch, again triggered by low pressure.

All three usually clear with a top-up. Here is how.

How to repressurise your Baxi boiler

You need the filling loop. It is a flexible braided hose with a valve at each end, usually tucked underneath the boiler.

1. Turn both valves to the off position to start.
2. Open one valve fully, then slowly open the other. You will hear water moving into the system.
3. Watch the pressure gauge. Stop when it reads around 1.5 bar.
4. Close both valves fully.

Do not leave the valves open. That keeps filling the system and puts it under too much pressure. Once you are back in range, the code should clear and the boiler return to normal.

Boiler keeps losing pressure after a top-up?

If you top up and the pressure drops again within days, you have got more than a one-off. Something is letting water or pressure out.

The usual suspects are a leak somewhere in the pipework or radiators, or a failed expansion vessel. Check radiators and visible pipes for damp patches. If you find a leaking radiator, close its valves to stop the water and get it looked at.

A leak you cannot see — under floors, inside walls — needs an engineer with the right kit. Same goes for a failed expansion vessel, which stops the boiler absorbing the normal rise and fall in pressure as the water heats and cools. If topping up has become a weekly job, book a repair rather than keep filling it — every top-up adds fresh, oxygenated water that corrodes the system faster over time.

Overheat and circulation faults — E110, E125 and E131

These codes are about heat and water flow inside the boiler, and they are engineer territory.

The Baxi E110 fault is an overheat lockout — the primary water has exceeded its maximum temperature, often because a jammed pump or trapped air has stopped the water moving as it should. The Baxi E125 fault is a circulation fault, meaning the water is not flowing properly through the primary circuit. The Baxi E131 fault code code is a flue overheat lockout, a related safety trip on the flue side.

Bleeding your radiators to clear trapped air is a reasonable first move on an overheat or circulation code. If that does not shift it, the fault is inside the boiler and needs diagnosing properly.

Gas, ignition and condensate faults — E133

The Baxi E133 fault means the boiler tried to fire and could not. Gas supply interrupted, ignition failed, or the flame was not detected.

Before you assume the worst, run two quick checks. First, is the gas actually on? Check other gas appliances in the house. On a prepayment meter, check there is credit. Second, in cold weather, E133 is very often a frozen condensate pipe. That pipe runs outside, and when it freezes and blocks, the boiler locks out.

Thawing a frozen condensate pipe is a safe home job. Pour warm — not boiling — water over the external plastic pipe, or hold a hot water bottle against it, until it clears. Then reset the boiler. If the gas is on and the pipe is not frozen, an E133 that will not clear needs an engineer. Anything to do with the gas valve, burner or ignition system is Gas Safe work.

Sensor faults — E20 and E28

Baxi boilers use NTC sensors to read temperature at various points. When one fails or reads out of range, you get a sensor code.

The Baxi E20 fault is a central heating sensor (NTC thermistor) fault. The Baxi E28 fault code is a flue sensor fault. Worth noting: like E133, an E28 in cold weather can also come down to a frozen condensate pipe, so thaw that first if it is freezing outside.

A genuine sensor fault means a component has failed and needs replacing. That is an engineer job — it involves getting inside the boiler and identifying the right part for your model.

Fan and control board faults — E160 and E168

Two more engineer-only codes, both about hardware inside the casing.

The Baxi E160 fault code is a fan fault. The fan clears combustion gases out through the flue, so the boiler will not run without it working properly. The Baxi E168 fault code is a PCB lockout — the printed circuit board, the boiler control brain, has tripped into a protective lockout state.

A single power cut can sometimes trigger a PCB lockout, so one reset is worth a try. If E168 sticks, or E160 shows at all, that is a diagnostic and parts job for a qualified engineer.

Baxi boiler flashing green

Not every light on a Baxi means trouble. A Baxi boiler flashing green light is usually a status indicator, not a fault. On many models a pulsing or flashing green light means the boiler is powered and in standby, or simply that there is no current demand for heat.

So before you panic, check whether it is actually a fault or just the boiler idling. If your thermostat is not calling for heat, a steady or slow-flashing green light is normal. If you are getting no heat or hot water when you should be, and the light behaviour looks wrong, that is when to look closer.

Baxi 105 HE fault codes

The Baxi 105 HE is one of the older HE-range models, and its codes do not always read the same as the current 600 and 800 boilers. If you have got one of these, do not assume a code means what it would on a newer unit.

Our guide to Baxi 105 HE fault codes covers the codes specific to that model so you are reading the right list. As with any older boiler, if parts are getting hard to source or faults are stacking up, it may be worth weighing a repair against a replacement.

Common Baxi boiler problems

Fault codes are not the only way a Baxi tells you something is wrong. No hot water, cold radiators, kettling noises, a boiler that keeps dropping out — plenty of problems show up without a clean E-code on the display.

Our rundown of common Baxi boiler problems walks through the faults we see most and what is behind them. It is a good starting point if your symptoms do not match a specific code, or if you just want to understand what your boiler is doing before you call anyone out. Age matters too — a boiler past ten or twelve years old will throw faults more often as parts wear, and at some point a string of repairs costs more than a replacement.

How to reset a Baxi boiler safely

Most Baxi models reset one of two ways. Either press and hold the dedicated reset button, or — on units with an on/off selector dial behind the pull-down flap — turn the selector to the "R" (Reset) position and hold it for around five seconds.

The golden rule again: reset once. If the code clears and stays clear, great. If it comes straight back, do not keep resetting. The boiler is telling you the fault is still there, and forcing it past a safety trip is how small problems become big ones.

When to call a Gas Safe engineer

Call an engineer when:

• A code returns after one reset.
• Pressure keeps dropping despite topping up.
• You see an overheat, circulation, gas, ignition, fan, sensor or PCB code.
• You smell gas, see scorching or soot near the boiler, or a CO alarm sounds — treat that as an emergency first, then call.

Anything behind the casing, on the gas circuit or in the electronics is engineer only by law. You can check any engineer registration, and the specific appliances they are qualified for, at the Gas Safe Register.

If you are in London and your Baxi has thrown a code you cannot clear, we can help. Our engineers handle Baxi boiler repair in London every day, across all the common ranges and fault codes.

Book a Baxi boiler repair

If the fix is not a simple top-up, it is worth booking sooner rather than later. A locked-out boiler in the middle of winter, or a fault that keeps repeating, tends to cost more the longer it is left.

Serviceteam is a Gas Safe registered, WHICH? Trusted Trader-endorsed company covering London. We offer free instant quotes, fixed pricing with no hidden charges, and fast callouts when your heating is down.

Book your Baxi boiler repair in London today, or get a quote online, and we will get your heating and hot water back on.