UNI-T UT366A Not Returning to Zero – Troubleshooting Malaysia

A UNI-T UT366A Digital Manometer should be checked under equal-pressure conditions before important measurements. If the display remains above or below zero when no pressure difference is applied, the result may contain a zero offset.

A non-zero reading does not always indicate sensor failure. Trapped pressure, connected hoses, airflow around the ports, temperature changes or moisture can also affect the displayed value.

Common Zero-Reading Symptoms

Users may observe:

The display remains positive with both ports open
The display remains negative with both ports open
The value changes slowly after disconnecting the hoses
The reading does not return to its original value
P1 and P2 show different behaviour
The offset appears after the instrument was dropped
The problem began after moisture exposure
The zero value changes when the hose is moved
The instrument differs from another verified manometer

Record the selected unit and displayed value before troubleshooting.

Disconnect Both Pressure Hoses

Begin by removing the pressure hoses from P1 and P2.

Both ports should be exposed to the same stable ambient pressure.

Check that:

No hose remains connected
No adaptor is trapping pressure
The ports are not covered
The instrument is away from direct airflow
The unit is not positioned in front of a fan or air-conditioning outlet
Nobody is blowing into either port

Allow the displayed value to settle before deciding whether an offset remains.

Move Away from Direct Airflow

An open pressure port can respond to moving air.

A reading may appear when the UT366A is placed:

Below an air-conditioning grille
Near an operating fan
Inside a ventilation duct
Beside an open window
In outdoor wind
Near an exhaust outlet

Repeat the zero check in a stable indoor area with no direct airflow.

Check for Trapped Pressure

Pressure may remain trapped inside a connected hose or fitting.

Possible causes include:

Pinched hose
Closed valve
Blocked adaptor
Kinked hose
Plugged test point
Moisture inside the line
Dust or dirt inside the hose

Disconnect all accessories completely and observe whether the reading changes.

Never insert sharp objects into the UT366A pressure ports.

Inspect the Pressure Ports

Check P1 and P2 for:

Physical damage
Cracks
Loose fittings
Dust
Moisture
Oil
Chemical residue
Signs of impact

The pressure ports should be protected from contamination.

Do not apply compressed air directly to the ports. Excessive pressure may damage the internal sensor.

Allow the Instrument to Stabilise

Moving the UT366A between areas with different temperatures may temporarily affect the reading.

Examples include:

Moving from an air-conditioned office into a hot plant room
Taking the instrument from a vehicle into a cold room
Leaving it under direct sunlight
Handling it after storage in a humid environment

Allow the instrument to stabilise in the test environment before repeating the zero check.

The stated UT366A operating range is 0°C to 50°C at up to 85% relative humidity.

Check the Battery Condition

The UT366A uses three AAA batteries and includes a low-battery indicator.

If the battery level is low:

Switch off the instrument.
Replace all batteries with a matching set.
Confirm correct battery polarity.
Restart the instrument.
Disconnect both hoses.
Repeat the zero check.

Inspect the battery compartment for loose or corroded contacts.

Confirm the Pressure Unit

A small offset can appear larger or smaller depending on the selected unit.

The UT366A supports units including:

kPa
mbar
bar
psi
mmHg
inH₂O
inHg
mmH₂O
ftH₂O
hPa

Record the unit together with the zero value. A number without its unit is not useful for assessment.

Check Whether the Offset Is Stable

Observe the zero reading for a short period.

Stable Offset

A value that remains consistently above or below zero may indicate:

Sensor zero shift
Temperature influence
Previous overpressure
Internal contamination
Calibration deviation

Moving Offset

A value that continuously changes may indicate:

Airflow around the ports
Moisture
Unstable temperature
Loose internal or external connection
Electronic instability
Pressure still trapped in an accessory

This distinction helps determine the next inspection step.

Did the Instrument Experience Overpressure?

The UT366A pressure range is ±15.00 kPa.

Applying pressure beyond the specified range may affect the internal sensor.

Possible overpressure symptoms include:

Permanent zero offset
Slow return to zero
Non-linear pressure response
Different behaviour between P1 and P2
Large difference from a reference
Reading remaining after pressure is removed

Stop using the instrument if overpressure damage is suspected.

Did Moisture Enter the Pressure Port?

Moisture may enter through a hose when measuring:

Condensing air
Wet ducts
Boiler or flue systems
Humid process lines
Systems without a suitable moisture trap

Possible symptoms include:

Slow response
Unstable zero
Reading that drifts
Pressure remaining after disconnection
No response from one port

Do not shake the instrument or blow compressed air into the port. Arrange inspection if liquid may have reached the internal sensor.

Compare with a Known Pressure Reference

If the UT366A returns to a stable zero but its accuracy is still uncertain, compare it with a suitable verified reference.

A controlled comparison can help identify:

Zero offset
Measurement deviation
Poor repeatability
P1 and P2 response differences
Possible calibration drift

Do not use a fluctuating HVAC system as the only reference for evaluating the instrument.

Checking, Calibration or Repair?

Checking identifies visible damage, hose problems, battery issues and basic instrument response.

Calibration compares the UT366A against a suitable pressure reference at selected measurement points.

Repair may be required when there is physical damage, moisture contamination, sensor failure or an electronic fault.

Calibration records measurement performance. It does not repair a damaged pressure port or sensor.

When Should the UT366A Be Submitted?

Arrange professional inspection when:

The display remains offset with both ports open
The zero offset is increasing
The instrument was dropped
Excessive pressure was applied
Moisture entered a port
P1 and P2 respond differently
Readings differ significantly from a verified reference
Battery replacement does not resolve the problem
The instrument is required for critical or documented testing

Do not open the instrument casing unless authorised to do so.

Information to Send for Initial Assessment

WhatsApp MTM Precision with:

A clear photo of the UT366A
A photo of the model and serial-number label
A photo showing both ports disconnected
A short video of the zero reading
The selected pressure unit
Details of any drop, overpressure or moisture exposure
The application in which the problem occurred

This information helps determine whether the issue is related to the setup, calibration condition or possible damage.

MTM Precision Sdn Bhd

Showroom & Service Centre:
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia

Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my