The control board is the brain of Tempra Plus — managing element power modulation, Flow Control logic, fault diagnostics, and the digital display. Failure is uncommon but possible after years of service or after voltage surges.
Symptoms of control board failure
- Display completely dead despite verified power at the unit
- Display lit but unresponsive to button presses
- Persistent unexplained fault codes that don\'t correspond to actual hardware issues
- Erratic element switching not matching control logic
- Smoke or burning smell from board area (visual confirmation of component failure)
- Visible burned components, swollen capacitors, or scorch marks
Diagnostic before replacement
- Verify 240V at unit power terminals — bad power supply mimics control board failure
- Verify control board power inputs — typically 24V or 12V DC at logic input pins
- Inspect for visible damage — burned traces, swollen capacitors, broken solder joints
- Verify sensor inputs reading normally — control board may report sensor faults that are actually wiring issues
- Confirm with Stiebel tech support before ordering — board diagnosis often happens by phone with multimeter readings
Replacement
Control board replacement is typically contractor work:
- Power off at all breakers; verify with voltage tester
- Open Tempra cabinet
- Photograph all connections and DIP switch positions before disconnecting
- Disconnect all leads from old board (label them)
- Remove old board from standoffs
- Install new board
- Reconnect all leads per photo/labels
- Set DIP switches per original board OR per Stiebel commissioning sheet
- Power up; verify display lit and responsive
- Set the model code via menu (Tempra-specific configuration)
- Test operation
Critical: model configuration
Stiebel control boards are platform-shared but require model-specific configuration after replacement. Without proper config, element wattage modulation will be incorrect — either underpowered (cool output) or overpowered (breaker trips, element damage). Stiebel tech support guides this configuration.
Cost
- Control board (OEM): $250-450 for Tempra Plus depending on model
- Contractor labor: $200-350
- Total: $450-800
- Within 3-year parts warranty: Stiebel covers part, homeowner covers labor
Bottom line
Control board failure is uncommon. Verify electrical and sensor health before suspecting the board. Always call Stiebel tech support before ordering — diagnostic guidance often saves the cost of an unnecessary board.