Hot Water System Error 11 🔥 Today one of my regular clients called me up saying his hot water system had stopped working and was showing Error Code 11. He wanted to replace the whole system straight away, but I suggested we do some quick checks first. Error 11 can sometimes be caused by a faulty regulator or a lack of gas supply — not always the system itself. I tested the gas regulator, which was all good, and confirmed the gas supply at the unit was sitting at 2.6 kPa, which is within range.