ᐅ The Vaillant VCW 196EC is experiencing intermittent operation issues.

Good morning,

a Vaillant Vcw 196EC heating system frequently stops working intermittently. It runs normally, and then, without any changes to the settings on the unit or the radiator thermostat, it displays the error E12. Sometimes also F40 or F23. Pressing reset stops the issue for hours. A new expansion tank and several other parts have been continuously replaced. It still needs to last a while... There is enough water in the system. What could this be?

Curiosius

Hi Curiosius,

With the Vaillant error codes E12, F40, and F23, it quickly becomes clear that the control unit seems to "lose track" somewhere – typically this involves either sensors, the circulation pump, or the communication between modules. If the expansion tank and various parts have already been replaced, I would suggest checking the circulation pump, especially since it sometimes stalls sporadically. The temperature sensors (flow/return) also tend to give incorrect readings due to slight corrosion residues or intermittent contacts, particularly with older piping.

Interestingly, these errors occur without changes to the settings, which strongly suggests an electrical issue or an intermittent short circuit in the control circuit. Also check whether the power supply is stable; especially with older devices, a fluctuating voltage phase can confuse the control unit.

I would be interested to know whether your heating circuits continue to run during the error messages or if they shut down completely. This helps to determine whether the control is "just measuring" or actually shutting down for safety reasons.

Good luck!

What do you mean by heating circuits now?

What do you mean by the question now?

Well, I heat both the air and the water... that?

If you mean the air and the water, it almost sounds as if you are considering the boiler more as an overall system rather than the actual circuits. The heat pump unit has a heating circuit and a separate domestic hot water circuit, and that’s exactly where strange errors often occur when the flow rate drops somewhere. Models like E12 and F23 are particularly sensitive to this, sometimes reacting to deviations of less than 20 percent. Have you checked whether the valves on the return flow are fully open, or if perhaps one valve is only partially open? Interestingly, this is often overlooked. Just as a side note, when the fault occurs, do you notice any change in the pump noise? That would be a clear indication.