Service & test modes: Combi Boiler tips

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

Start the flue test (chimney sweeper) function

FlowMax · FLOWMAX-120 condensing combi

Runs the unit at maximum heating output without modulation for 15 minutes so you can take combustion readings.

1. Hold the Service button for 7 seconds to start the function.
2. Take the combustion readings within the 15 minutes.
3. Press the unit OFF button to stop it early.

Force a fixed firing rate with DIP switch 1

Navien · NCB-250/150H, NCB-240/130H, NCB-240/110H, NCB-190/080H, NCB-190/060H

Switches 1 and 2 of the first DIP bank hold the burner at minimum or maximum for testing; leave them OFF/OFF for normal operation.

1. Turn power off before removing the front cover to reach the DIP switches.
2. 1 ON, 2 OFF = 2-stage MAX.
3. 1 OFF, 2 ON = 1-stage MIN.
4. 1 ON, 2 ON = 1-stage MAX.
5. Return 1 and 2 to OFF/OFF for normal operation.

Force minimum or maximum firing (special operations)

Navien · NCB-250/150H, NCB-240/130H, NCB-240/110H, NCB-190/080H, NCB-190/060H

Special operations hold the burner at a fixed rate for gas pressure and CO2 checks; they return to normal after 3 hours with no input.

1. Hold Back and Menu together for 3 seconds and choose 7. Special Operations.
2. Normal returns to normal operation.
3. 1st MIN / 4. 2nd MIN: minimum firing (low-fire CO2 / offset).
4. DHW 1st MAX / 5. DHW 2nd MAX: DHW maximum firing.
5. SH 1st MAX / 7. SH 2nd MAX: SH maximum firing (inlet gas pressure, high-fire CO2).

Purge air from the heating piping (Air Purge Mode)

Navien · NCB-250/150H, NCB-240/130H, NCB-240/110H, NCB-190/080H, NCB-190/060H

Air purge mode ends by itself after 15 minutes.

1. Hold Back and Menu together for 3 seconds and choose 8. Air Purge Mode.
2. Choose 1. SH pipe air purge.

Run test mode (fan, pumps, valves, venturi)

Navien · NCB-250/150H, NCB-240/130H, NCB-240/110H, NCB-190/080H, NCB-190/060H

Test mode switches individual outputs so you can check them one at a time.

1. Hold Back and Menu together for 3 seconds and choose 6. Test Mode.
2. Fan Motor ramps the fan up to top speed and back down.
3. 2-5. Boiler / Zone 1-3 pumps toggle on/off (zone pumps only in pump system).
4. 6-8. Zone 1-3 valve output toggles (zone valve system only).
5. 3 Way Valve Output toggles the 3-way valve.
6. Flow Control Valve / 11. Mixing Valve drive open-closed-back and show FEEDBACK.
7. Dual Venturi / 13. Recirc. Pump toggle on/off.