If there is a reading of 5 PPM turn off the gas to the heater and advise them to contact a HVAC repair service. Turn on the dryer and let it run for a few minutes. Take a reading by the vent. If the reading of 5 PPM, turn off the gas and advice them to contact an appliance repair service. If it puts out over 5 PPM, advise the resident to let the fire burn out and contact a chimney sweep to check the fireplace.
Range Turn on the oven and all the burners on the range.
If there is more than 800 PPM CO at start-up and more than 400 PPM CO at normal operation, turn off the gas and advise them to contact an appliance repair service. Check the heater the same as you would a fireplace. Regardless of the reading advise the resident the fire service considers space heater a serious hazard and encourage resident not to use them. Once the source of the CO has been found, advise the resident and open the window to air out the house. If the resident aired out the house before our arrival, or if no source was found, you can create a worst-case scenario.