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Guide · Gas detection · Honeywell BW MAX XT II how-to

How to calibrate a Honeywell BW MAX XT II (GasAlertMax XT II): the pump test, zero and span, what ERR and the error screens mean, how to turn it off, how often to calibrate, and the calibration gas, regulator and hose it takes

To calibrate a Honeywell BW MAX XT II: activate it in clean air with the diffusion cover on (the pump will not run its start-up test without it), then press and hold the button through the OFF countdown and keep holding through the CAL countdown; the detector auto-zeroes the LEL, H2S and CO sensors and calibrates the oxygen sensor, and when APPLY GAS shows you connect the hose from a 0.5 L/min or demand flow regulator on the quad cylinder to the pump inlet; the span runs about two minutes and ends at CAL DUE. The manual asks for a bump test before each day’s use, a calibration at least every 180 days, and a hose no longer than 3 ft for calibration. "ERR O2" is the oxygen sensor failing its self-test or zero, and this page covers what to do.

Bayshore Safety. Industrial safety and PPE supplier since 2017. · Current as of November 2026 · Honeywell BW MaxXT II user manual (129541-L3 Rev G: activation and deactivation, startup tests, pump test, calibration guidelines and procedure, alarm set points, troubleshooting, specifications) and quick reference guide; the Honeywell BW MaxXT II product page and the IntelliDoX datasheet (automation.honeywell.com, fetched Nov 10 2026)
MAX XT II detectors and the parts this guide namesGas detection selector
BW Technologies XT-XWHM-Y-NA Max XT II 4-Gas Monitor, LEL/O2/H2S/COBW Technologies XT-XWHM-Y-NA Max XT II 4-Gas Monitor, LEL/O2/H2S/COHoneywell BW lists the MAX XT II at 13 hours per charge, IP66/67, a pump that samples through up to 75 ft of hose, and a two-year warranty including all sensors
$1,174.64See the product

Why the MAX XT II gets its own page. It is the Honeywell BW detector with the pump, the one that draws a sample from a manhole, tank or pit through a hose before anyone goes in, and the pump adds steps the MicroClip page does not have: the start-up pump test, the block test, the pump alarm, the hose length limits and the filters. The questions people ask (how do I calibrate it, what is ERR O2, what does error code 02 mean, how do I reset it) are answered in the BW MaxXT II user manual, and this page quotes it. The parts the manual names are in the band at current prices.

The MAX XT II, question by question

Quotations are from the BW MaxXT II user manual (129541-L3 Rev G).

What is the MAX XT II, and what does it detect?A four-gas detector with an integral sample-draw pump: LEL (SR-W-MP75 sensor, 0 to 100 percent LEL), oxygen (SR-X2V), hydrogen sulfide (SR-H-MC) and carbon monoxide (SR-M-MC), sold in configurations from the single-gas versions to all four; XWHM is the four-gas unit, XUHM the version with the unfiltered LEL sensor, and the -CS kit adds the confined space case. Honeywell BW lists 13 hours of battery at 20 °C (8 hours at −20 °C) with a 6-hour charge, IP66/67, a 95 dB alarm, a pump rated for up to 75 ft (22 m) of hose, datalog storage of 375 hours at 15-second intervals, and a full two-year warranty including all sensors. Approvals as printed: UL Class I, Div 1, Group A, B, C, D; ATEX II 1 G Ga Ex ia IIC T4; IECEx Ga Ex ia IIC T4.
How do I turn the MAX XT II on and off?The manual: "Ensure the diffusion cover is attached prior to activating the detector to verify the pump is working correctly. To activate the detector, press the button in a safe area that is free of hazardous gas. Attach any pump accessories to the detector prior to activating." To turn it off: "press and hold until the OFF countdown completes." The start-up runs fourteen tests in order: battery, audible/visual, firmware version, start-up message, location logging (a site number 1 to 999 if enabled), pump test, alarm set points (TWA and STEL for H2S and CO, then LOW and HIGH for every sensor), self-test, auto zero for H2S, CO, O2 and LEL, calibration due date, force calibration, cal IR lock, bump test, sensor and power test, and the last-calibration and last-bump screens. "Confirm these tests occur."
What is the pump test, and what if the pump fails?With the diffusion cover attached the pump starts at activation; in the cold the screen counts down a warm-up. "If the Force Block Test option is enabled, the detector performs a pump test": the screen asks you to block the end of the hose with a finger, and "if the hose is not blocked and unblocked within 2.5 minutes, the detector will assume the pump has failed and deactivates." A passed test shows a confirmation screen; a failed one shows the failure screens and the detector deactivates, and you activate it again before going to troubleshooting. If the cover is off, the detector beeps and shows a screen until it is replaced, then raises a pump alarm that you acknowledge with the button. In use, "the pump draws air over the sensors continually. If the pump stops operating or becomes blocked, the detector activates the pump alarm": HIGH shows with the pump symbol flashing, which "displays the same as a high alarm, except that [the pump symbol] flashes", so check for a pump alarm before clearing a hose; clear the blockage and press the button, and with Force Block Test on the detector re-tests the pump. The hydrophobic pump filters (XT-RF-H5 and the 50 and 100 packs), the particulate pump filter (GA-PFMAX) and the pump kit (XT-RPUMP-K1) are the service parts.
How do I calibrate a MAX XT II, step by step?The manual’s guidelines: calibrate only in a safe gas-free area; not during or immediately after charging; a used sensor stabilizes 60 seconds and a new one 5 minutes; calibrate at least every 180 days; use a cylinder within date; the maximum hose length for calibration is 3 ft (0.9 m); and either a 0.5 L/min manual regulator (REG-0.5) or a demand flow regulator (REG-DF-1). Connect: regulator on the cylinder, calibration hose on the regulator. Procedure (section 6.4): 1. Activate the detector. 2. Make sure the sensors to be calibrated are enabled in Safety Suite Device Configurator. 3. Verify the gas matches the span values set in the detector. 4. "Press and hold while the detector performs the OFF countdown. Continue to hold as the detector briefly deactivates. The detector then reactivates and performs the calibration countdown. Continue to hold until the countdown is complete." (Release early and it turns off.) 5. Auto zero: "Do not apply calibration gas until Apply Gas displays, otherwise the auto zero function will fail"; the detector zeroes the combustible and toxic sensors, calibrates the oxygen sensor and beeps twice. 6. Auto span: at APPLY GAS, "attach the hose quick connector to the pump quick connector to apply gas"; after 50 percent of the gas is detected on all sensors (within 30 seconds) the span runs about two minutes; a passed span beeps and goes on to the calibration due date screen. Press the button at any time to abort.
Why does the span fail?The manual lists exactly when the detector will not span a sensor: "gas is not applied to the sensor; 50% of the expected gas concentration is not detected within the first 30 seconds; or the gas concentration drops below 50% of the expected gas level during the 2-minute span." If gas was applied and it still fails: repeat with a new cylinder, then with a new 0.5 L/min or demand flow regulator, then with a new hose; if excessive target gas is present at zero the sensor fails the zero instead, so move to clean air. A sensor that fails "retains the previous span value" and its due date does not reset; a sensor that keeps failing is replaced (the sensor part numbers are in the band) and calibrated before use. The demand flow regulator has inlet limits the manual prints: disposable cylinders 0 to 1,000 psig, refillable 0 to 3,000 psig.
What calibration gas does the MAX XT II use?The same mixes as the MicroClip: CO 100 ppm balance N2, H2S 25 ppm balance N2, LEL 50 percent (2.5 percent methane in North America, 2.2 percent in the EU) balance air, and O2 18 percent (clean air for the zero). The manual names the 34 L cylinder CG-Q34-4 and the 58 L CG-Q58-4, premium-grade and certified to national standards, and warns that "the calibration gases must meet the accuracy of the detector". With the IntelliDoX dock (DX-MAXXT) the gas goes through a demand flow regulator on the dock.
How often should the MAX XT II be bump tested and calibrated?The manual calls for a bump test before each day’s use "to confirm their ability and response to gas by exposing the detector to a gas concentration that exceeds the high alarm setpoints. Verify that the audible and visual alarms activate. Calibrate if the readings are not within the specified limits." Calibration: "at least once every 180 days, depending upon use and sensor exposure to poisons and contaminants", at a new sensor, and when the ambient reading varies at start-up. The intervals are set per sensor in Safety Suite Device Configurator; the detector ships with Force Bump disabled and Force Calibration available, and with either forced option on, an overdue detector will not run until the test passes (and deactivates if the forced calibration fails).
What does ERR O2 or "error code 02" mean on a GasAlert MAX XT II?There is no numeric code; "02" is O2. The manual: "The detector tests for missing or defective sensors during the startup self-test and continuously thereafter. If a sensor fails the self-test, Err displays above the gas type of the failed sensor", and "after the detector enters normal operation, ERR displays if a sensor has" failed. ERR O2 is the oxygen sensor failing its self-test, its auto zero at start-up or its span. To reset it: acknowledge the alarm with the button, let the sensor stabilize (60 seconds used, 5 minutes new), reactivate in clean 20.9 percent air so the auto zero on start-up can calibrate the O2 sensor, and run a calibration; if ERR returns, replace the SR-X2V oxygen sensor and calibrate it. With Lockout on Self-Test Error enabled (the detector ships with it disabled) a failed sensor stops activation until it is replaced. "Err" over LEL, H2S or CO follows the same path with that sensor.
How do I reset the MAX XT II, and how do I clear a latched or TWA alarm?A gas alarm clears itself when the concentration drops below the low set point; "if alarms are set to latch, press [the button] to reset the alarms"; the pump alarm and the Due Today alarms (calibration, bump test, pump block test) are acknowledged with the button, and a low alarm can be acknowledged (audible alarm silenced temporarily) only if Low Alarm Acknowledge is enabled in Safety Suite Device Configurator. TWA and STEL alarms stop either by deactivating and reactivating the detector or by clearing the TWA, STEL and MAX readings: press the button twice rapidly to page through the time and date, TWA, STEL and MAX screens to CLEAR ALL and press again, with the manual’s caution to confirm with your supervisor first. There is no factory reset on the keypad; set points and options are changed in Safety Suite Device Configurator (default login administrator / Default123 as the manual prints it, to be changed).
What are the factory alarm set points?The manual’s sample factory set points "as defined by OSHA", varying by region: O2 19.5 percent low and 23.5 high; LEL 10 percent low and 20 high; CO 35 ppm low, 200 high, 35 TWA, 50 STEL; H2S 10 ppm low, 15 high, 10 TWA, 15 STEL. "To disable an alarm, set the alarm setpoint to 0 (zero)" in Safety Suite Device Configurator. The TWA uses the OSHA 8-hour moving average and the STEL a 5 to 15 minute user-defined interval.
How long is the hose, and how long does the battery last?Sampling: "The maximum hose length for sampling is 75 ft (22 m)" (the HOSE1-75 in the band); calibration: 3 ft maximum. The longer the hose the longer the draw before the reading is true, so wait before judging a space. Battery: one rechargeable lithium polymer pack gives 13 hours at 20 °C and 8 hours at −20 °C; first and normal charges are 6 hours, in a safe area; the battery indicator may take hours to show on a deeply discharged pack and the manual says 8 hours before calling it defective. The replacement pack is the XT-BAT-K1 and the charger the XT-C01-MC5.
What are the specifications and what does it cost?From the specifications section: lithium polymer battery, 13 hours; calibration by automatic zero and automatic span; datalog 375 hours at 15-second intervals; a 6-hour charge; the temperature code and approvals above; the diffusion cover, calibration cap and hose, quick connectors and filters as accessories. The price is per configuration (four-gas in yellow or black, unfiltered-LEL version, confined space kit, single- and multi-gas versions) and is on each row in the band.
Can the MAX XT II be bump tested in a dock?Yes: Honeywell lists the BW MaxXTII among IntelliDoX-compatible detectors, with its own module (DX-MAXXT) and nest; the dock bump tests, calibrates and configures the detector and transfers its logs over USB or Ethernet, and Honeywell describes it as the method that avoids purge cycles that waste gas.

The MAX XT II in plain words

  • Diffusion cover on before activation, or the pump test does not run; hose no longer than 75 ft for sampling and 3 ft for calibration.
  • One button: hold through OFF to turn off; hold through OFF and CAL to calibrate; press to acknowledge latched, pump and Due Today alarms.
  • Bump before each day’s use with gas above the high set points; calibrate at least every 180 days and after any sensor change.
  • Gas: CO 100 ppm, H2S 25 ppm, LEL 50 percent, O2 18 percent; CG-Q34-4 or CG-Q58-4 cylinder; 0.5 L/min or demand flow regulator.
  • A span fails if 50 percent of the gas is not seen within 30 seconds or drops below 50 percent during the two-minute span; new cylinder, new regulator, new hose, then the sensor.
  • ERR above a gas is a failed sensor; "error 02" is ERR O2, the oxygen sensor; stabilize, zero in clean air, calibrate, replace.
  • Factory alarms: O2 19.5/23.5, LEL 10/20 percent, CO 35/200 ppm, H2S 10/15 ppm, adjustable.
BW MaxXT II user manual (129541-L3 Rev G). Fetched Nov 10 2026.

Questions people ask

How do I calibrate my Honeywell BW MAX XT II 4-gas detector?

Activate it with the cover on, hold the button through OFF and then CAL, let it auto-zero, and at APPLY GAS connect the hose from the regulator on the quad cylinder to the pump inlet; the span runs about two minutes and ends at CAL DUE.

What does error code 02 mean on a GasAlert MAX XT II?

There is no code 02; it is ERR over O2, the oxygen sensor failing its self-test or zero. Acknowledge, stabilize, reactivate in clean air, calibrate, and replace the SR-X2V sensor if it repeats.

My MAX XT II displays an ERR O2 error. How do I reset it?

Press the button to acknowledge, let the sensor stabilize, turn the detector off and on in clean 20.9 percent air so the start-up auto zero runs, then calibrate; a sensor that fails again is replaced and calibrated.

How do I turn off a MAX XT II?

Press and hold the button until the OFF countdown completes; release it early and the detector stays on.

How often should a MAX XT II be calibrated?

At least every 180 days, with a bump test before each day’s use, per the manual.

What calibration gas does the MAX XT II use?

The quad mix (100 ppm CO, 25 ppm H2S, 50 percent LEL, 18 percent O2) in the CG-Q34-4 or CG-Q58-4 cylinder through a 0.5 L/min or demand flow regulator and a hose no longer than 3 ft.

What is the pump test on a MAX XT II?

A start-up check that the pump draws: with Force Block Test on, you block the hose end with a finger within 2.5 minutes and the detector confirms the pump; without the cover the test cannot run.

Why is my MAX XT II showing HIGH with a flashing pump symbol?

That is the pump alarm, not a gas alarm: the pump is blocked or stopped. Clear the hose, press the button, and let the block test re-run.

How long a hose can the MAX XT II sample through?

75 ft (22 m) as the manual states; the HOSE1-75 is that length. Calibration hose is limited to 3 ft.

What are the specifications of the Honeywell BW MAX XT II?

Four gases (LEL, O2, H2S, CO), integral pump, 13-hour battery with a 6-hour charge, IP66/67, 95 dB alarm, 375 hours of datalog, Class I Div 1 and ATEX/IECEx Ex ia IIC T4, two-year warranty including sensors, as Honeywell BW prints them.

What is the price of the Honeywell BW MAX XT II?

Per configuration; the current price is on each row in the band, with the confined space kit priced separately.

What are the MAX XT II factory alarm set points?

O2 19.5 and 23.5 percent, LEL 10 and 20 percent, CO 35 and 200 ppm, H2S 10 and 15 ppm, with TWA and STEL on the toxics; adjustable, and set to zero to disable.

Does the MAX XT II work with IntelliDoX?

Yes, with the DX-MAXXT module; the dock bump tests, calibrates and configures it and transfers the logs.

Related guides

Bump test vs calibrationWhat each does and how oftenGas detection for confined space entryWhat to test and the orderWhat is calibration gas?And how to choose the right cylinderHow to calibrate a Honeywell BW MicroClip XLBump test, calibration, error messages and turning it offHow to calibrate and bump test an MSA ALTAIR 5XZero, span, the pump test and the sensor-life warningIs H2S heavier than air?And where it collects

The ratings, test results and standards shown here are the manufacturers' published values, reproduced as published. Nothing on this page is a recommendation by Bayshore Safety that any product is suitable for a particular task, hazard or workplace. Selecting safety products and protective equipment is the responsibility of the end user and the employer, based on their own hazard assessment and the regulations that apply to their work. Confirm every value on the manufacturer's own documentation before use.

Need monitors matched to the gases on your permit?Call (925) 215-7337 or email us the gases in your hazard assessment and where people work, and we will quote the monitors, calibration gas and docks with the manufacturer figures listed. We service and calibrate portable gas instruments and sell nationwide.
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