This paper addresses the problem of scheduling the cleaning actions of a heat exchanger undergoing fouling and ageing. The existence of two discrete layers leads to the use of two cleaning methods which differ in their ability to remove the aged layer. A mixed integer nonlinear programming (MINLP) model is presented and solved for three case studies with different ageing rates. The optimal schedule consists of: (i) the timing of the cleanings and (ii) the cleaning mode in each instant. (c) 2011 Elsevier Ltd. All rights reserved.