Baxi 800 Combi 2 E.01.20 fault code: maximum flue-gas temperature reached

If your Baxi 800 Combi 2 displays E.01.20, Baxi defines it as “Maximum flue gas temperature reached.” The boiler has detected that the measured flue-gas temperature has reached its permitted maximum and has stopped normal operation to protect the appliance.

This is not a code to solve by opening the boiler or checking the flue yourself. The combustion circuit, flue, sensors and internal components must be assessed by a Gas Safe registered engineer. Your useful role is to keep the boiler closed, record the exact code and note what happened immediately before it appeared.

What E.01.20 means

A modern condensing boiler monitors temperatures as it operates. The flue carries combustion products safely away from the appliance, while the boiler’s controls use sensor information to keep operation within designed limits. E.01.20 means the boiler has detected the maximum flue-gas temperature threshold being reached.

Baxi lists E.01.20 for its Combi and System 2 range, including the Baxi 800 Combi 2. Fault codes vary by range, so do not rely on an explanation for an older Baxi model or another manufacturer. Confirm “Baxi 800 Combi 2” from the appliance information and report the code exactly as shown.

What you may notice

The boiler may stop firing, leaving you without heating, hot water or both. It may have been operating normally and then shut down, or the code may return when demand becomes higher. You could notice the boiler starting and stopping, but that behaviour alone cannot identify why the temperature limit was reached.

There may be no visible sign outside the appliance. Do not assume that an apparently clear external flue terminal proves the whole flue path is sound. Equally, do not reach, climb or dismantle anything to inspect it. An engineer has the equipment and access needed to test the appliance safely.

What can lead to this code?

E.01.20 identifies a high-temperature condition; it does not name a single failed part. An engineer may need to consider heat transfer through the boiler, water circulation, combustion performance, the flue system, deposits or restrictions, and the accuracy of the temperature sensing and control system.

Reduced heat transfer or water movement

If heat is not being carried away from the boiler as designed, temperatures can rise. The cause could relate to circulation, a restriction or the condition of internal heat-transfer surfaces. These are professional checks, not a reason to flush, dismantle or clean the boiler yourself.

Flue or combustion-related conditions

The flue and combustion system are safety-critical. An engineer may inspect their condition and verify the appliance’s combustion performance. Never loosen a flue joint, remove a panel or block an air opening. Work on a gas appliance must be carried out by someone competent and appropriately registered.

A sensor or control issue

The boiler relies on temperature sensors and electronic controls. If a reading is inaccurate or a control is not responding correctly, the boiler can stop and show a fault. Proper testing is needed before any component is condemned or replaced.

Safe checks before booking a repair

There are only a few sensible homeowner checks. Copy the full E.01.20 code, note whether the heating or hot water was running, and record whether the display showed another message first. Check the boiler pressure from the normal gauge or screen without removing any covers.

• Confirm the thermostat and programmer settings are normal.
• Look for visible water leaks around the appliance and accessible pipework.
• From ground level only, note any obvious external obstruction near the flue terminal, but do not touch or dismantle it.
• Check whether a carbon monoxide alarm has activated.
• Record whether the fault followed repeated starting and stopping or a period of heavy demand.

Do not try to cool the boiler with water, remove the case, alter gas controls or interfere with the flue. Those actions can create serious risks and may obscure the evidence an engineer needs.

Should you reset E.01.20?

Follow only the Baxi user instructions supplied for your exact boiler. If those instructions permit a user reset, make one attempt. If E.01.20 returns, stop resetting and arrange a repair. Repeatedly clearing a safety shutdown does not correct the cause of excessive temperature.

If the boiler restarts, treat that as useful information rather than proof of a permanent cure. Note how long it operates and what demand was present when the code came back. If it continues to work, monitor it closely and still report any recurrence.

When the situation is urgent

Stop using the boiler and seek urgent help if you smell gas, a carbon monoxide alarm sounds, there is scorching, smoke, unusual heat around the appliance, or water is reaching electrical parts. If you smell gas, avoid flames and electrical switches, leave the building and contact the National Gas Emergency Service.

Carbon monoxide has no colour, taste or smell. Headache, dizziness, nausea, breathlessness, collapse or loss of consciousness can be warning signs. Move into fresh air and seek immediate medical help if exposure is suspected. The appliance should not be used again until it has been checked and made safe.

If the boiler simply stops with E.01.20 and none of those emergency signs is present, it still needs timely professional attention. A related guide on a boiler that keeps turning itself off explains why repeated shutdowns should be recorded rather than continually overridden.

What an engineer may check

A Gas Safe registered engineer can inspect the appliance, review fault history and test the factors that influence flue-gas temperature. This may include water circulation, heat transfer, sensors, combustion readings and the flue arrangement. The checks will depend on the condition of your installation and the evidence found on site.

Giving the engineer the exact code, model, timing and recent symptoms can shorten the path to the correct repair. Mention any recent work on the heating system, changes in boiler behaviour or recurring pressure problems. Keep the casing closed and leave internal testing to them.

Quick answers

What does Baxi E.01.20 mean?

It means the boiler has detected that the maximum flue-gas temperature has been reached.

Is it safe to keep resetting the boiler?

No. Follow the model-specific user instructions for a single permitted reset. If the code returns, arrange a professional repair.

Does the code prove the flue is blocked?

No. The code reports a temperature condition, not one confirmed cause. The flue is one of several areas an engineer may need to assess.

Can I inspect the flue myself?

You can note an obvious external obstruction from a safe position, but do not climb, dismantle joints or remove the boiler case. Flue and combustion checks are professional work.