Service & test modes: Tankless Water Heater tips

Short, practical technician tips on service & test modes for tankless water heater. Check each one against the manual for your exact model before acting.

Purge the exhaust circuit (P9 menu)

Bosch · Greentherm T9800 SE 160/199 and T9900 SE 160/199 tankless water heaters

About 2 seconds after entering the menu the fan starts and keeps running until the menu is left.

1. Open Information / Adjustments, touch until P9 Purge shows
2. Touch the symbol to start; the fan starts after about 2 seconds
3. Exit the menu to stop the fan

Read live operation data (OD menu)

Bosch · Greentherm T9800 SE 160/199 and T9900 SE 160/199 tankless water heaters

OD shows live readings for troubleshooting: heat exchanger outlet/inlet/outlet NTCs, air pressure, fan speed, water flow, ambient and exhaust NTCs, external tank temperature, barometric pressure and ionization value.

1. Open P4 Information and select OD Operation Data
2. Touch the symbols to scroll through the readings

Read the last 10 error codes (FH failure history)

Bosch · Greentherm T9800 SE 160/199 and T9900 SE 160/199 tankless water heaters

FH shows the last 10 error codes; three dots mean no error has occurred. The date symbol shows when an error happened.

1. Open P4 Information, select FH Failure History
2. Touch up or down to move between stored errors
3. Touch the date symbol to see the date and hour of an error

Force minimum or maximum firing (special operations)

Navien · Navien NPE-A2 (built-in recirculation) and NPE-S2 condensing tankless water heaters: NPE-150S2, NPE-180A2/S2, NPE-210A2/S2, NPE-240A2/S2

Special operations hold the burner at a fixed firing rate for combustion checks.

1. Hold Menu and Back together for 3 seconds and choose 4. Special Operations.
2. Pick 1st MIN, 1st MAX, 2nd MIN or 2nd MAX.
3. Choose 1. Normal to return to normal operation.

Run test mode (fan, flow valve, venturi, pump, mixing valve)

Navien · Navien NPE-A2 (built-in recirculation) and NPE-S2 condensing tankless water heaters: NPE-150S2, NPE-180A2/S2, NPE-210A2/S2, NPE-240A2/S2

Test mode drives individual parts so you can check them one at a time.

1. Hold Menu and Back together for 3 seconds and choose 3. Test Mode.
2. Fan Motor: fan ramps from 0 to max and back, repeating.
3. Water Flow Adjust Valve: full open to full close over about 12 s, shows 0-100%.
4. Dual Venturi: on when entered, Up/Down toggles on/off.
5. Pump (A2) / Ext. Pump (S2): runs 10 s, stops 5 s, 5 times (75 s).
6. Mixing Valve (S2 only): full open to full close over about 10 s, shows 0-56%.

Trial operation of parts (EZ Start Plus app)

Noritz · EZ, NRCR, CDV (Pro units with EZ Start Plus app)

Switch individual parts on and off to check them: fan motor, igniter, water servo, pump (NRCR only) and bypass servo (CDV only), depending on the unit.

1. Open EZ Start Plus and connect.
2. Tap Maintenance, then Trial Operation.
3. Pick the part and tap the toggle to turn it on, tap again to turn it off.

Enter performance data view

Rinnai · Rinnai tankless water heaters (SENSEI and Non-SENSEI series)

Opens the performance data list so you can read live operating values from the unit.

1. Press and hold the Down button.
2. While holding Down for 2 seconds, press and hold the On/Off button too (both buttons held together).
3. Use the Up and Down buttons to scroll to the data item you need.
4. Read the value shown for that item. Units are listed in the performance data table.

Start descaling (vinegar flush) mode on the PC board

Rinnai · Rinnai SENSEI RX/CX tankless (RX, RXP, CX, CXP)

Button B on the PC board brings up dES; pressing A starts the flush cycle.

1. Remove the front panel and locate pushbuttons A and B on the PC board (controller blank).
2. Press B for 1 second and release when dES appears.
3. Press A: dES starts blinking and the flush cycle is running.
4. Circulate vinegar through the unit; the display then counts down from 60 (minutes), shows rnS (rinse), then End.

View diagnostic code history

Rinnai · SENSEI and Non-SENSEI series

Shows the last 9 maintenance codes, which flash one after another.

1. Turn the water heater off with the On/Off button.
2. Press and hold On/Off for 2 seconds, then press Up at the same time.
3. The last 9 maintenance codes display and flash in turn.
4. To exit, press and hold On/Off for 2 seconds, then press Up at the same time.
5. Turn the water heater on with the On/Off button.