Baxi Boiler Fault Codes
Baxi Boiler Fault Codes Explained
This guide breaks down the most common Baxi boiler fault codes by category, explaining what each one means, what usually causes it, what you can try first, and when it is time to call a Gas Safe registered engineer. Bookmark this page for the next time your boiler flashes up a code.
Water Pressure and Temperature Faults
What caused it?
System pressure has dropped below the minimum the boiler needs to run safely, usually around 0.5 bar. This is often caused by a small leak somewhere in the pipework, a recent radiator bleed that was not topped back up, or a slow weep from a valve that has gone unnoticed. It is one of the most common Baxi boiler fault codes homeowners see, and usually the easiest to put right yourself.
What to do?
- Locate the filling loop, usually a braided hose underneath the boiler.
- Open both valves slowly and watch the pressure gauge rise.
- Stop once the gauge reaches around 1.0 to 1.5 bar.
- Close the valves fully, then reset the boiler.
Do I call an engineer?
O Only if the pressure keeps dropping again within a few days. A boiler that needs repressurising every week or so almost always has a leak that needs finding and fixing properly.
What caused it?
System pressure has risen above the safe operating range, often from overfilling during a previous repressurisation or a fault with the expansion vessel that normally absorbs pressure changes as water heats up.
What to do?
- Bleed a small amount of water from a radiator using a bleed key.
- Watch the pressure gauge drop back towards 1.0 to 1.5 bar.
- Reset the boiler once the pressure looks correct.
Do I call an engineer?
Yes, if the pressure keeps climbing again shortly after bleeding it down, since this points to a failing expansion vessel or filling loop.
What caused it?
The boiler has detected the water temperature climbing above a safe level, often because the pump has jammed, air is trapped in the circuit, or the safety thermostat sensor has tripped.
What to do?
- Let the boiler cool down fully before touching anything.
- Bleed any radiators that feel cold at the top.
- Reset the boiler once and see if it fires normally.
Do I call an engineer?
Yes, if it happens more than once. A jammed pump or a faulty sensor will not fix itself with repeated resets.
What caused it?
The flue system has overheated and the boiler has locked out as a safety precaution, sometimes linked to restricted airflow around the flue terminal or a wider overheat issue elsewhere in the boiler.
What to do?
- Check the flue terminal outside is not blocked or obstructed.
- Avoid repeated resets.
Do I call an engineer?
Yes, this needs a proper inspection of the flue and burner.
Ignition and Flame Faults
What caused it?
The boiler failed to establish a flame within the expected time. In cold weather this is very often caused by a frozen condensate pipe, the small plastic pipe that carries waste water outside, rather than a genuine fault with the boiler itself. It can also point to a gas supply issue, a low prepayment meter balance, or a worn spark electrode.
What to do?
- Find the condensate pipe where it exits the property, usually white plastic.
- Pour warm, never boiling, water over any visibly frozen section.
- Check the gas supply is on and other gas appliances are working.
- Check any prepayment meter has sufficient credit.
- Reset the boiler after thawing and check it fires normally.
Do I call an engineer?
Yes, if the fault returns after thawing the pipe and confirming the gas supply, since this needs proper diagnosis.
What caused it?
The boiler has lost its flame repeatedly, typically around twelve times, and has locked out to protect itself. This can relate to gas pressure, the flue, or a failing ignition component.
What to do?
- Try a single reset from the control panel.
- Note whether it happens at a particular time of day, which can hint at gas pressure issues.
Do I call an engineer?
Yes, repeated flame failure should always be looked at by a professional rather than reset repeatedly.
What caused it?
The sensor monitoring flue temperature has tripped its safety limit, which can point to restricted airflow, a failing sensor, or a wider overheat issue.
What to do?
- Check the flue terminal outside for any obvious blockage.
- Avoid repeated resets.
Do I call an engineer?
Yes, the flue and sensor will need checking properly.
What caused it?
The thermistor that monitors flue temperature has failed or given an unreliable reading, sometimes alongside a frozen condensate pipe in cold weather.
What to do?
- Check for and thaw a frozen condensate pipe if it is winter.
- Reset the boiler once after checking.
Do I call an engineer?
Yes, if the fault persists once the condensate pipe has been ruled out.
Sensor (NTC) Faults
What caused it?
Water is not circulating through the heating system properly, so the boiler cannot distribute heat effectively. This is often caused by trapped air, a partially blocked pipe, or a pump that is struggling.
What to do?
- Bleed every radiator, starting with the ones furthest from the boiler.
- Check the system pressure is still in the normal range afterwards.
- Reset the boiler once you have bled the system.
Do I call an engineer?
Yes, if bleeding the radiators does not clear it, since this may point to a failing pump or sludge in the system.
What caused it?
The sensor that reads the central heating flow temperature has failed, worked loose, or developed a wiring fault.
What to do?
- Reset the boiler once, as a loose connection can occasionally reseat itself.
- Avoid repeated resets if the fault returns immediately.
Do I call an engineer?
Yes, the sensor or its wiring will need testing and is likely to need replacing.
What caused it?
The return sensor, which reads the temperature of water coming back into the boiler, has failed or lost its connection.
What to do?
- Reset the boiler once to see if the fault clears.
Do I call an engineer?
Yes, this needs proper testing with diagnostic equipment.
What caused it?
The boiler's self-test of the flow and return sensors has failed, which can point to a wiring issue or a sensor reading outside its expected range.
What to do?
- Reset the boiler once.
- Note the exact code shown for the engineer.
Do I call an engineer?
Yes, this is a sensor-level fault that needs proper diagnosis.
Fan and PCB Faults
What caused it?
The fan is not reaching, or is not holding, the speed the control board expects. This can be a wiring issue, a failing capacitor, or the fan itself starting to wear out.
What to do?
- Try one reset from the boiler's control panel.
- Listen for any unusual grinding or rattling from the boiler.
- Avoid repeating the reset if the fault comes straight back.
Do I call an engineer?
Yes, the fan or its wiring will usually need checking and possibly replacing.
What caused it?
The printed circuit board that controls the boiler's electronics has detected a fault with itself or a connected component.
What to do?
- Try a single reset from the control panel.
- Avoid repeated resets, as they will not fix a genuine PCB fault.
Do I call an engineer?
Yes, this usually points to a faulty printed circuit board that needs professional diagnosis.
What caused it?
This code often appears after another fault has already occurred and been reset, and the boiler could not confirm what caused the original problem. It can also point to a power supply that is fluctuating above or below the normal 230V range.
What to do?
- Think back to whether a different code showed just before E168 appeared.
- Reset the boiler once by turning it off and on again.
- Check nothing else on the same circuit is causing power fluctuations.
Do I call an engineer?
Yes, if the fault repeats or you cannot identify an earlier code, since this needs proper diagnostic testing.
Power and Gas Valve Faults
What caused it?
The boiler has received a mains voltage lower than around 195V, which is outside its normal operating tolerance and can be caused by wider issues with the property's electrical supply.
What to do?
- Check whether other appliances in the property are also affected.
- Reset the boiler once the supply looks stable again.
Do I call an engineer?
Yes, if it keeps happening, since this may need an electrician as well as a heating engineer.
What caused it?
A wiring fault on the gas valve (E09) or a poor connection to the gas valve (E15) is stopping the boiler from controlling gas flow correctly.
What to do?
- Do not attempt to open the casing or inspect the valve yourself.
- If you smell gas at any point, leave the property and call the National Gas Emergency Service on 0800 111 999.
Do I call an engineer?
Yes, immediately. Both are gas safety faults and should be treated as urgent.
If Your Baxi Boiler Shows a Different Format
What caused it?
Pressure in the heating circuit has dropped below the acceptable range, similar to E119 on older models. This is a "blocking" code, meaning the boiler may restart on its own once the pressure is corrected.
What to do?
- Top up the pressure via the filling loop to around 1.0 to 1.5 bar.
- Check for any obvious leaks around visible pipework.
Do I call an engineer?
Only if the pressure keeps dropping again within a few days, which points to a leak.
What caused it?
The boiler's controls are expecting a signal from an outdoor temperature sensor, used to adjust heating output automatically, but cannot detect it. This usually means a wiring or connection issue rather than a fault with the boiler itself.
What to do?
- Check the sensor cable has not come loose if it is visible and accessible.
Do I call an engineer?
Yes, the sensor and its wiring will need testing.
What caused it?
On simpler models such as the Main Eco Compact and Main Eco Heat, a single red flash typically indicates a sensor or flow fault rather than a numeric code. The exact meaning depends on the colour and number of flashes shown.
What to do?
- Check your model's manual to confirm what the specific flash pattern means.
- Reset the boiler once if the manual suggests it is safe to do so.
Do I call an engineer?
Yes, sensor and flow faults on these models are not a DIY fix.
Trust BAXI Boiler Experts
Baxi's own fault code system changes from range to range, E-codes on one model, A-codes or flashing lights on another, and reading Baxi boiler fault codes correctly at a glance saves an unnecessary call-out. That kind of detail only comes from working on these boilers day in, day out.
Our Gas Safe registered heating engineers service and repair Baxi boilers across homes throughout Essex, from a straightforward E119 pressure reset to a full E168 lockout that needs proper diagnostics. We carry genuine Baxi parts on the van wherever we can, so most repairs are sorted in a single visit.
What to Do?
Safe DIY Checklist
- Note the exact code or flash pattern shown, since Baxi uses E-codes, A-codes, H-codes and flashing lights depending on the model
- If it is an A-code, wait a few minutes first, as "blocking" faults can sometimes clear on their own once the cause passes
- Check boiler pressure is within the normal range, usually around 1.0 to 1.5 bar when cold
- In cold weather, check the condensate pipe outside for ice, a very common trigger for E133
- Check any prepayment gas or electricity meter has enough credit
- Confirm the gas supply is switched on and other gas appliances in the property still work
- Reset the boiler once, but stop if the same code comes straight back
Avoid opening the boiler casing or attempting any internal repairs. If a fault code returns after working through this checklist, it is time to call a Gas Safe registered engineer.