Step function in a time-dependent problem

Hello everyone,

I am trying to implement a step function in my time-dependent problem where I want to lower the temperature of a constant temperature boundary from 40°C to 20°C after 10min (600s) of running the model. However, I always get the error "Failed to find consistent initial values. Last time step is not converged." Running the model without the step function works.

The details of my step function are: Location 600, From 0, To 1. Implemented into the constant temperature boundary like this: T0 = 40 - (20*step1(t)) [degC]

Thanks for your help!