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A disgruntled customer is suing Nest(s goog), claiming that the company’s popular line of home thermostats are defective because they heat up and fail to measure a room’s actual temperature.

In a complaint filed this week in San Jose, Maryland man Justin Darisse said he bought the device on Amazon for $249.99 after seeing Nest promotional videos that suggested it would save him money, but that faulty temperature readings caused him to actually pay more for energy costs:

Nest’s base and faceplate heat up, which causes Nest’s temperature reading to be from two to ten degrees higher than the actual ambient temperature in the surrounding room. This defect prevents the thermostat from working properly. As a result, Nest users do not experience the advertised energy savings.

The lawsuit, which asks a court grant class action status, points to video images like the one below to claim Nest did not work as promised:

The complaint seeks more than $5 million on behalf of hundreds of thousands of other Nest buyers over alleged the company’s alleged violation warranty and consumer protection laws. Nest, which was acquired by Google in January, declined to comment.

Nest has won plaudits for its stylish design and use of smart sensors to improve home energy efficiency. If the lawsuit is successful, however, it could hurt its reputation among cost-conscious consumers like Darisse, who stated that “he would have continued to use his traditional Honeywell Thermostat that retails for around $30.00″ had he known about the alleged defect.

According to the complaint, many Nest customers have taken to online comment boards to complain about different temperature readings between Nest devices and other home thermostats. It also states an advertising body told Nest to stop making certain claims such as a promise that its device can “cut AC runtime up to 30 percent.”

You can read the complaint, which was spotted by Law360, for yourself here (I’ve marked up some of the relevant bits):

This story was updated at 3:44pm ET to say that the complaint seeks at least $5 million, not $500 million, from Nest.

Nest Class Action

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