// bench playbook · BP-003 · plumbing
Tankless E11 within 48 hours of a flow-sensor clean — the bench playbook.
A 12-year-old Rinnai keeps throwing E11 inside two days of a flow-sensor cleaning. The sensor is the right swap. The read is in the wrong place.
A 12-year-old Rinnai RU model throws E11 inside forty-eight hours of a flow-sensor cleaning. The board code is the symptom; the diagnosis lives in the inlet temperature against the sensor's resistance curve at the 6 °C ↔ 4 °C swing — a 6 °C inlet reading on a sensor spec'd to a 4 °C curve throws the same code as a genuinely failed sensor. A board-side bench read will not see that difference.
Rinnai spec'd the flow sensor to a 4 °C inlet reference. Local winter inlet sits closer to 6 °C at the meter. The sensor reads in spec at shop ambient; under live inlet, the resistance curve shifts and the board declares a fault the part does not have. The third truck roll is not going to fix that with another sensor in inventory.
Truck rolls × hourly
3 × 1.6 hr × $140/hr
Sensor stock
$46
Warranty write-off
~$620
bench move
Before authorizing the third visit, the bench reviewer asks the tech for two field measurements at the actual inlet temperature, not at shop ambient.
- 01Meter the flow-sensor Ω at the actual inlet temperature running through the unit during a draw — not in the truck, not on the bench.
- 02Pull the manifold pressure under a 2-gpm demand cycle for 90 seconds; a clean sensor reading does not move manifold pressure.
- 03Watch E11 over a 10-minute observation window with the unit under repeated draws at varying flow rates.
- 04Hand back water-resistance vs. inlet-temperature readings to the bench as a small tape — three to five entries, labeled by draw.
// Send the setup brief
Bring us the ticket that already cost you a callback.
The intake is four fields; an owner reads every one within one business day. We will tell you straight if your line is not a fit for the $997 setup before you spend money.
// 4 fields · owner reads every one · reply within one business day
Related playbooks
// 2 more
- BP-001 · HVACbench playbook
No-cool callback after a capacitor swap that would not hold.
The dual-run cap reads in spec at the truck, then droops under pull-down. Three truck rolls in ten days. One bench move that closes the loop.
- BP-002 · appliancebench playbook
E15 on a dishwasher — the control board reorder that did not hold.
Three warranty callbacks in three weeks. The board keeps coming back. The float switch never got metered under a dry-cycle drain test before the reorder.
// Signoff
— secondshift-3. The bench is the difference between a ranked guess and a verifiable verdict on a $4,000 part swap. Each playbook in this column came out of one.