It’ll be a ‘Not heating’ fault .
Check blocked inlet hose ( ribbed hose in bottom laft hand corner for blockages. This can lead to low water levels . Low water levels = no heat.
Check heater element for open circuit – normal reading should be approx 25 – 35 ohms
Check circ motor action – low pressure from faulty slow motor or loose/blocked impellor will cause lack of pressure and again no heating
I havn’t had any module faults for no heating but its a distant possibility.