What 3121 Means
The RTD is the cavity temperature sensor that every cooking decision depends on. Wolf's M Series Troubleshooting Manual logs 3121 when the upper cavity's RTD reads as a short circuit and 3122 for the lower, both at priority 2. The resistance the board sees is far too low to be a real oven temperature, so it stops heating rather than work from it.
Common Causes of 3121
- An RTD sensor that has shorted internally after years of heat cycling
- Moisture or cleaning fluid bridging the sensor terminals at the rear of the cavity
- A harness that has chafed through and is shorting to the oven frame
🔧 One Safe Check You Can Try
Cast your mind back over recent cooking - things burning sooner than they used to, or an oven that claimed to be at temperature far too fast. A sensor drifting toward a short usually misbehaves before it fails outright.
⚠ Why You Shouldn't Go Further Than That
- The sensor plugs in behind the oven's rear panel, which means drawing a heavy built-in unit out of its cabinet before anything is visible.
- A shorted sensor and a shorted harness read identically at the board, so both ends get ohmed rather than one being assumed.
- RTDs are specified by resistance curve, and a physically similar sensor with the wrong curve will bake badly while showing no problem.
Opening a panel to inspect or repair something yourself doesn't automatically cancel your manufacturer's warranty — but it can risk accidental damage, and some manufacturers do have specific service conditions. Check your product's warranty terms, or ask us, before deciding.