ThermoTop V: Unexplained Error Troubleshooting

Hi.

I have a TT-V unit that aborts the start process shortly after it activates the glow plug. It then goes into emergency mode. The error memory only shows "Error 152" (read via the W-bus). Normally, all errors are explained, but this one is not. I've tried everything, but I just can't find a reason for it. The glow plug/flame sensor, blower, and water pump seem to be working correctly, and since the metering pump is not even activated, it cannot be the problem.

Does anyone know what this error message means?

/Jan