<div>Hello ESP-r community I am modelling a passive ventilation system with the air flow facility in ESP-r. In my system I have a heat exchanger with the characteristics dP = 5.6e-3 x m + 4.8e-5 x m^2 This calls for a quadratic flow component type 20 or 25 to model the heat exchanger in my system. However using any of the two causes this error message: Please check (in the following order) that:  - each node has some flow path to a boundary pressure and  - iteration convergence control is not too strict Day xx Month xx Hour xx: 100 iterations; flow solution failed Using power law components (e.g. 10, 15 or 17) does not generate this error message and I can't find the iteration convergence control (for integrated simulations). What am I doing wrong? I am using esp-r version 11.2 from learnix. <div>Best regards Christian Anker Hviid Civil engineer ALECTIA A/S Teknikerbyen 34 \ 2830 Virum \ Denmark Tel: +45 88 191 000 \ Dir. tel:  +45 88 191 365 Mob: +45 40 879 749 \ <a href="http://www.alectia.com">www.alectia.com</a> </div></div>