Express Delivery to Your Door, Worldwide!


VMC (Voice Multi Control) Cold air blowing during normal start


  • The heat exchanger is cold - not warm from the previous heating cycle.
  • After cold normal start, the fan starts and continues spinning.
  • The diesel fuel pump does not start (no ticking sound) .
  • Only two icons appear in the bottom part of LCD display: 
  • (A) HEATING - the icon of 3 arrows pointing upward. 
  • (B) FAN - the propeller icon.
  • No other icons appear initially or afterwards in the bottom part of the screen.
  • The heating process is not initiated and the unit only blows cold air. 

* All of the above criteria must be met to qualify for this recall.


Model: HEATPORT H2 / H4 / H4 Hybrid

Controller: VMC (formerly Voice Multi Control)


Date of manufacture: Late 2021 to Early 2022

Type of thermal sensor: 50k NTC / green wires / metal cap between sensor and the exchanger


Faulty thermal sensor attached to the heat exchanger

Solution: Exchange thermal sensor

other possible causes of the same symptom

Hot Exchanger from previous heating cycle

Solution: Cool down the exchanger and start again.

Faulty ECU module *

Solution: Exchange the ECU module.

Why is this happening

The sensor works on the principle of changing resistance based on the temperature. It is a 50k NTC thermistor (thermally sensitive resistor with negative temperature coefficient). The sensor should be providing resistance +-50kOhm during the room temperature (about 25°C). If the thermistor is faulty, it provides an incorrect resistance. As the resistance is in the allowed range, the controller would not provide any error code but instead the measurement is classified as hot heat exchanger. This causes the fan to spin and blow the cold air through the exchanger.


You may experience the symptoms described above. To confirm your NTC sensor is faulty, your sensor would be out of the specified characteristics.

* Note, the characteristics apply for the 50k NTC sensor only. The 1k PTC sensor has a different characteristics.

Are all MENTIONED MODELS affected?

No. Only the limited number of heating units that were assembled with the sensor from the affected production batch were affected. Under normal circumstances these sensors should last years with no failure and in ideal scenario for the whole life-time of the product. All affected heating units went through quality checking and passed - confirming the correct functionality of the sensor at the time of testing. The failure of the sensor can not be identified at the time of the test and usually happens after first few weeks/months/year of operation of the product always with the same result - dropping the resistance down from its nominal value.

Is this a safety issue/risk?

No, the fault of the sensor adjusts the resistance to the negative direction instead of positive. In different words, the system reads the temperature of the exchanger as "too hot" and activates the cooling down procedure at the time when the unit is cold and should be already prepared for new heating cycle. This cooling-down procedure never ends. HEATPORT also does not record a single case where the faulty sensor would provide opposite characteristics or provide the safety risk or caused a damage to 3rd party. However we recommend replacing the sensor when above symptoms appear.

What has heatport done to prevent this fault on new UNITS H2 / H4 / H4 Hybrid?

After identifying the incorrect batch of the sensors, we have started assembling the units with another model of the sensors from another manufacturer. The units already put into stock have been reassembled with the new sensors. We have also started assembling the units with new PTC sensor (Positive temperature coefficient) from our new supplier.  These two new sensors are more stable and should not cause any other issues in future.

What has HEATPORT offered as a solution to affected products?

Free supply of the more stable replacement sensor or free supply and refitting to customers who can visit the HEATPORT workshop in Cheviot / North Canterbury.

How difficult is to replace the sensor?


1) Spring wire

2) Thermal sensor

This process is very straightforward and can be carried by the end customer in about 5 minutes. The replacement does not require a skilled technician or any special tools. The replacement also does not require the heating unit to be removed from the installation bottom plate as long as there is suitable access from the top of the main heating unit.



1) Please switch off the heating unit (in case its hot, wait until it cools down)

2) Disconnect the main power supply

3) Remove the round cap on the intake side of the heating unit by turning anticlockwise OR remove the 60/75mm intake duct hose by removing the hose clamp first.

4) Remove the top plastic lid. For the lids with the 2 plastic clips attached to the bottom part of housing, lift these first by putting the finger underneath until it clicks. Make sure you do not break these clips, you must do this carefully.

5) Use a Phillips or Hex screwdriver and unscrew the socket screw holding the main ECU unit (PCB board enclosed in the plastic housing).

6) Push together the two black plastic springs attached on the vertical plastic pole behind the fan turbine that hold the ECU in the locked position and lift the ECU up for full access to all connectors.

7) Locate the connector of the thermal sensor and disconnect it from ECU. Take a picture (makes it easier to match the pinouts).

8) Use the flat screwdriver and unhook the spring wire pushing the sensor to the top of the exchanger.

9) Match the pinout of the previous sensor

    - Check the exact pinout of the original sensor.

    - You must connect one of the wires to the white terminal according to the previous sensor as different versions of ECU have different pinout.

10) Exchange the overheating sensor.


11) Please follow the above sequence IN REVERSE to reassemble the heating unit.

12) Turn on the heating unit.


All ECU boards are compatible with 50k NTC sensor, but pinout may be slightly different. You may have different versions based on the production batch. You can check the version of your ECU printed on the PCB board (this requires lifting the ECU module from the heating enclosure). Only one version is compatible with the new PTC sensor.

50k NTC compatible ECU

v 2.71 - uses 2 pin connector

v 3.1 - uses 3 pin connector

v 3.6 - uses 3 pin connector

v 3.7 - uses 3 pin connector

50k NTC / 1k PTC compatible ECU

v 3.7 (MK2) - PCB uses 3 pin connector

How to identify the compatible PCB (all conditions must be met):

- PCB has written: MAINBOARD v3.7

- small 5pin unused connector in left bottom corner

- PT & NTC written next to the 3 pin connector for the thermal sensor

How can I get the replacement?

If your heating unit is affected by the fault described above let us know and we will ship you a free replacement sensor.

Get new sensor >

Generate URL