Police have warned people to beware of conmen who may be selling stolen boilers at bargain prices.
The boilers, taken from a lock-up in Gravesend, Kent, are only compatible with the gas main system in the Channel Islands.
They are highly dangerous if used in mainland UK, police said.
The owner of the Sun Lane lockup discovered the 40 boilers were missing on Monday when he found the door of the premises had been forced open.
Detective Chief Inspector Colin Croucher said: "People may be buying them thinking they are getting a bargain but they would actually be putting themselves and their families at risk if they are used.
"I would urge anyone who is offered such a model or knows of anyone selling them to contact us immediately."
The boilers are Vailant wall-mounted models.