The plumber will perform a negative pressure test, he will check the gas isolation valves and any LPG cylinders plus associated components to make sure they are not leaking. He will check all landlord supplies gas appliances. An example of a landlord supplied gas appliance is a gas cooktop or a gas heater. He will also conduct a gas combustion spillage test to identify if CO (carbon monoxide) is present in the property. He will record all this data into a report, which makes up part of the compliance reports.