Debonding in ground heat exchangers used with geothermal heat pumps may occur for a variety of reasons, such as shrinkage of the backfill materials or surrounding formation, improper grouting and thermal mismatch. The effect of thermal contact resistance on the heat conduction due to debonding in ground heat exchangers was investigated using a set of one-dimensional simplified analytical models as well as two-dimensional finite element models. From the cases studied, debonding at the backfill/pipe interface was found to be of greater significance than debonding between grout and surrounding formation.