The Baxi E.00.20 fault code means the flue gas temperature sensor is not connected or has measured a temperature below its range. Those are the two possibilities in Baxi’s current wording. The code alone does not tell a homeowner which one applies.
The message concerns the boiler’s monitoring of flue-gas temperature. It is not proof that the sensor itself has failed, and it does not by itself mean that the flue is blocked. Because the sensing system relates to combustion and the flue, internal checks must be left to an appropriately qualified Gas Safe registered engineer.
Which Baxi boilers show E.00.20?
Baxi’s current error-code information lists E.00.20 for a model group that includes the Baxi 200, 400, 600 and 800 Combi 2; Baxi Assure 500 Combi 2; Baxi 600 and 800 System 2; and Baxi Assure 500 System 2.
Error-code tables can cover several related products, so confirm the full model name from the front-panel label or your paperwork. Do not remove the boiler casing to find it. Giving the exact model to the engineer helps them use the correct technical information.
What does the flue gas temperature sensor do?
At a homeowner level, the sensor provides the boiler control with information about temperature in the flue-gas path. The boiler compares that information with the operating conditions it expects.
E.00.20 is displayed when the control sees either no recognised connection to that sensor or a temperature reading below the expected measuring range. The message identifies the detected condition, not the root cause. Similar-looking symptoms can arise from different electrical or appliance conditions, which is why a visual guess is not enough.
Does E.00.20 mean the flue is blocked?
No. Baxi’s wording for this code is about the flue gas temperature sensor being unconnected or recording below range. It does not state that the flue is blocked. Equally, a clear-looking external terminal does not rule out a problem elsewhere.
You can look at the outside flue terminal only from a safe, normal ground-level position. Do not climb, remove a cover, touch the terminal or try to clear anything from it. Never put an object into a flue. If the flue cannot be viewed safely, leave it alone.
Safe checks before arranging repair
- Record the complete code exactly as displayed, including the dots.
- Confirm the full boiler model without removing any panels.
- Note whether heating, hot water, or both have stopped.
- Write down any other code shown before or after E.00.20.
- Note whether the message followed servicing, other work or a power interruption.
- If safely visible from ground level, note any obvious damage around the external flue terminal without touching it.
Do not open the casing or inspect the flue, combustion area, sensor, connector, wiring or circuit board. Do not take resistance, voltage or continuity readings. These are not homeowner checks, even if an online video makes them appear straightforward.
Can I reset a Baxi E.00.20 fault?
If the user guide for your exact model permits a reset, you may try one reset using those instructions. Baxi uses different control layouts and reset methods, so use the correct guide rather than copying a sequence for another boiler.
If the code returns, do not keep resetting the appliance. A persistent signal problem needs professional attention, and repeated resets will not repair it. Tell the engineer whether the code returned immediately or after the boiler tried to operate.
When is E.00.20 urgent?
Turn the boiler off using its normal user control and seek prompt professional help if you notice unusual fumes, scorching, repeated shutdowns or visible damage around the appliance or flue. Do not investigate inside the boiler.
If you smell gas, suspect carbon monoxide, feel unwell around the appliance, or a carbon-monoxide alarm sounds, leave the property, avoid electrical switches and naked flames, and follow the Gas Safe Register’s emergency guidance. Call the National Gas Emergency Service on 0800 111 999 from a safe place.
What information helps the engineer?
Share the exact E.00.20 code, the model name, what the heating and hot water are doing, any accompanying codes and the timing of any recent work or power loss. A photograph of the display can help if it can be taken without opening or touching the appliance.
The engineer can then carry out the appropriate checks safely. Avoid naming a failed part in advance: the manufacturer’s two-part wording deliberately leaves more than one detected condition open.
For other plain-English explanations, visit the boiler help hub.
Is Baxi E.00.20 stopping your heating or hot water?
Book a fixed-price boiler repair aimed at fixing the fault, with the booking price clear before the visit.
Quick answers about Baxi E.00.20
What does Baxi E.00.20 mean?
It means the flue gas temperature sensor is not connected or has measured a temperature below its range.
Does E.00.20 prove the sensor is faulty?
No. The code reports a detected condition and includes two possible descriptions. A qualified engineer must establish the cause.
Does E.00.20 mean the flue is blocked?
No. That is not the manufacturer’s stated meaning for this code.
Can I inspect the flue or sensor?
No. Do not open the boiler, touch the flue or test the sensor circuit. Only make a ground-level external observation if it is safe.
Should I repeatedly reset the boiler?
No. Try one reset only if the exact model guide allows it. If E.00.20 returns, arrange repair.