CO sensor connection

I am testing the MQ CO sensor linked below

https://www.zeroohm.com/carbon-monoxide-sensor-mq-7/?search=gas

I am measuring the analog output at the end of the 5v cycle,
just before switching the Heater voltage to 1.5volt

I connected 1.5v battery to the NC terminal of the relay and
5v to the NO terminal of the relay and I am using the relay to switch the heater voltage between 5v and the 1.5v. Please check the attachment.

The LED is switching ON correctly according to the assigned time in the program, however, the contacts of the relay does not move. I discovered this when I measured the heater voltage. I always get 5 volts.

When I tested the relay directly with the with the 5v and ground of Arduino, I could hear the switching of the contact, in your opinion, what could be the problem?

Your text description does not match the picture you posted.

... I connected 1.5v battery to the NC terminal of the relay and 5v to the NO terminal of the relay ...

The picture shows the opposite connection.

For me it looks like the voltage drop over the diode in the +5V trail is to big (usually 0,7V or more depending on the diode). This may cause the relay not to work as expexted. In conjunction with the resistor of 220 ohms you are also limiting the current to less than 20mA...depending on the type of relay this might not be enough...

I will remove the 220 and the LED resistor. I only added them to visualise the timing of which the heater voltage is 5v or 1.5 v.

After removing the resistor and the LED, now the relay contacts works correctly