Thieves stole newly-fitted boilers after breaking into three properties on a Kettering building site.
The incidents happened between 6.30pm on Thursday, April 6 and 8.30am on Friday, April 7.
Three properties on the Kier construction site on Westhill were forcibly entered.
Offenders stole newly-fitted boilers from the first two but nothing from the third.
It is believed they entered the site by climbing over the fence from the adjacent wasteland.
Witnesses, or anyone with information, are asked to contact police on 101 or Crimestoppers anonymously on 0800 555111.