This error can occur when boiler is following ANK indoor outdoor reset parameters at ODT below 0 deg. C. Change menu functions by pressing the screwdriver symbol. Enter password 030 by using the arrow keys. Confirm password by pressing the screwdriver key again. The Moducontrol display will indicate # 1. Using the arrow up key scroll to position # H Ati. Using the screwdriver key enter the parameter. Existing parameter should read 65 deg. C. Change parameter by using the down arrow and toggle key to 50 deg.C. Confirm the new setting by pressing the screwdriver key. Exit from program menu by pressing the textbook key. Also check the design temperature boiler return (inlet) water setting. Set for 45 to 50 deg. C.