Service & test modes: Boiler tips

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

Force minimum or maximum output for 15 minutes (function 2.F)

Bosch · Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Temporary test mode: 00 normal, 01 minimum output for 15 minutes, 02 maximum output for 15 minutes. The boiler returns to normal after 15 minutes or when aborted.

1. Open service functions with the service button and scroll with key pad lock / ECO
2. Select 2.F, choose 01 or 02, save

Lock the boiler at minimum or maximum output (function 9.A)

Bosch · Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Values: 00 normal, 01 permanently minimum output, 02 permanently maximum output. The display shows 9.A while active.

1. Reach the second level (service button, then ECO and key pad lock together) and scroll to 9.A
2. Choose 01 or 02, and set 00 to return to normal

Move the 3-way valve to centre to drain (function 7.b)

Bosch · Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

After value 01 is saved the 3-way valve moves to its centre position so the system can be drained and the motor removed. Leaving the function resets it to 00.

1. Open service functions with the service button and scroll with key pad lock / ECO
2. Select 7.b, set 01 and save

Read the latest stored fault code (function 6.A)

Bosch · Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Shows the most recent fault code stored in the boiler. Read-only.

1. Open service functions with the service button and scroll with key pad lock / ECO
2. Select 6.A to read the code

Start or stop the building drying program (function 7.E)

Bosch · Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Starts and stops the slab drying program. While it is on, the gas settings cannot be adjusted.

1. Open service functions with the service button and scroll with key pad lock / ECO
2. Select 7.E to start or stop it

Start the air-purge routine (function 2.C)

Bosch · Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Starts the air purge by hand, for example after servicing. Values: 00 off, 01 purge once then back to 00, 02 permanently on.

1. Open service functions with the service button and scroll with key pad lock / ECO
2. Select 2.C and press the emissions test button
3. Choose 01 and save by holding the emissions test button

Start the emissions test (chimney sweep) mode

Bosch · Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Holding the emissions test button starts boiler test mode for gas pressure and combustion checks; a brief tap toggles between maximum set heating output and maximum nominal output.

1. Keep the emissions test button pressed until it lights
2. Tap it to switch between max set heating output and max nominal output
3. Keep it pressed until the light goes out to return to the supply temperature

Test ignition with continuous sparking (function 8.F)

Bosch · Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Gives continuous sparking without gas to test the ignition parts. Never leave it on for more than 2 minutes at a time because it can damage the ignition transformer.

1. Reach the second level (service button, then ECO and key pad lock together) and scroll to 8.F
2. Set 01, test, then set 00

Display test

Glow Brand · All C95 and C140 units

Lights every LCD segment so a faulty display can be checked.

1. Open the User Menu and select parameter 0.997.
2. Confirm and watch that all LCD segments light up.
3. Press any button to quit.

Read error history and live data (Information Menu 1.000)

Glow Brand · B85, B120, B160 (NG and LP)

The information menu is read-only and does not need the installer code.

1. 051 = last 16 lockouts, 1.052 = last blocking error, 1.031 = last error number.
2. 008 = flame current in uA (needs more than 1.5 to keep the burner on).
3. 053 flame failures, 1.054 successful ignitions (x16), 1.055 failed ignitions, 1.056/1.057 burner hours CH/DHW (x10), 1.058 total run days.
4. 040-1.043 actual, ignition, minimum and maximum fan RPM; 1.033 CH pressure; 1.006 flue temperature; 1.063 0-10 V input.

Run the system test (fixed fan / low / ignition / high fire)

Glow Brand · B85, B120, B160 (NG and LP)

Parameter 0.200 appears in the user menu only after the installer code has been entered. Used for combustion setup; the boiler locks in CH mode so a heat load must be available. It times out on its own.

1. Enter the installer code in CodE, leave the installer menu and open the user menu (0.000).
2. Select 0.200. The main screen shows tESt alternating with the active test.
3. Step through tests with CH up/down or DHW up/down: OFF, FAN (fixed fan speed), Lo (minimum power), Ign (ignition power), Hi (maximum power), REg (maximum power limited by supply temperature), Stb (max thermostat test), LCO1 (low water cut-off test).
4. For combustion analysis pick Hi, wait 5 minutes, measure CO2/CO at the 1/2 in. test port in the exhaust adapter, then check Lo as well.

Pump service mode to purge air

HTP · EL-80, EL-110, EL-150, EL-220, EL-299, EL-399 (N/LP)

Run each pump by hand to bleed the system.

1. Disconnect the wires on the THERMOSTAT terminals
2. Apply power
3. Press the down arrow and ENTER together for 1 second: CH pump runs
4. Press the up arrow: DHW pump; again: system pump (cascade master)
5. Down and up together returns to normal

Test mode (fixed-fire, gas pressure and combustion)

HTP · EL-80, EL-110, EL-150, EL-220, EL-299, EL-399 (N/LP)

Run the boiler outside normal modulation.

1. Create heat demand by opening zones
2. Press the up arrow and ENTER together for 1 second
3. Boiler goes through ignition, then use up/down to raise or lower fan speed (SERVICE RUN rpm)
4. Exit with up and down arrows together; exits by itself after 20 minutes

Force a fixed firing rate with DIP switch 1

Navien · Navien NHB-H condensing boilers: NHB-150H, NHB-110H, NHB-080H, NHB-055H

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 · Navien NHB-H condensing boilers: NHB-150H, NHB-110H, NHB-080H, NHB-055H

Special operations hold the burner at a fixed rate; they return to normal automatically after 3 hours.

1. Hold Back and Menu together for 3 seconds.
2. Choose 7. Special Operations.
3. Pick Normal, 1st MIN, 1st MAX, 2nd MIN or 2nd MAX.

Purge air from the heating or DHW piping (Air Purge Mode)

Navien · Navien NHB-H condensing boilers: NHB-150H, NHB-110H, NHB-080H, NHB-055H

Air purge mode returns to normal by itself after 15 minutes.

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

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

Navien · Navien NHB-H condensing boilers: NHB-150H, NHB-110H, NHB-080H, NHB-055H

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

1. Hold Back and Menu together for 3 seconds.
2. Choose 6. Test Mode.
3. Pick the output: fan motor ramp, boiler/system/zone/DHW pumps, zone valves or dual venturi.

Checking spark and gas valve voltage during ignition

NTI · Trinity Tft60, Tft85, Tft110, Tft155, Tft175, Tft200, Tft250, Tft300, Tft399

What to measure while the control is in its trial for ignition.

1. Measure 120 VAC from J5-6 to ground for the spark generator
2. Measure 24 VAC from J5-2 to J4-10 for the gas valve
3. Look for the arc through the observation port next to the spark electrode in the burner door

Reading the lockout and alert history

NTI · Trinity Tft60, Tft85, Tft110, Tft155, Tft175, Tft200, Tft250, Tft300, Tft399

The control keeps the 15 most recent lockouts and the 15 most recent alerts. Look there first whenever something seems off.

1. On the Summary page touch the History button
2. Read both the lockout log and the alert log before changing anything

Running a pump by hand

NTI · Trinity Tft60, Tft85, Tft110, Tft155, Tft175, Tft200, Tft250, Tft300, Tft399

Quick way to find out whether the control or the pump is at fault.

1. Open the pump diagnostic page on the display
2. Switch the pump on manually
3. Measure for 120 VAC at the pump terminals on the line voltage strip

Start test mode for manual firing

NTI · TRX boiler

Test mode runs the boiler at a fixed output and can be started from the parameter menu or by holding Reset. It ends by itself after 30 minutes or when Reset is pressed.

1. Open the complete menu and go to parameter 2.7.0.
2. Choose TEST+ for maximum heating power, maximum DHW power, or minimum power.
3. Or hold the Reset button for 10 seconds to start test mode.
4. Press Reset to end test mode early, or wait 30 minutes for it to stop.

Turning the burner switch back on

NTI · Trinity Tft60, Tft85, Tft110, Tft155, Tft175, Tft200, Tft250, Tft300, Tft399

If the Summary page shows the burner switch off as the demand, the control is not allowed to fire.

1. Open the Diagnostics pages
2. Go to the burner test page and switch the burner on

View the error history

NTI · TRX150

The HISTORY button shows the last 10 errors stored by the boiler.

1. Press the HISTORY button.
2. Scroll through the stored errors.
3. Note the codes before clearing any lockout.

Force the burner on for combustion checks (SERV function 1)

Rinnai · E50CRN; E75CRN; E75CRP; E110CRN; E110CRP

SERV chapter test functions: 1 = burner at adjustable load, 2 = fan, 3 = pump, 4 = showroom mode. Function 1 is what you use for the O2 / CO2 check and the ionization reading.

1. Enter C123, press MODE until SERV
2. Press STEP to pick function 1
3. Raise the load with +; hold - to go down to OFF, which ends the test
4. Target O2 at minimum 4.4 % on natural gas, 4.8 % on propane; ionization at least 4 uA

Ignition safety test (forced E02 lockout)

Rinnai · E50CRN; E75CRN; E75CRP; E110CRN; E110CRP

Proves the flame-failure lockout works. Expect one start plus four retries, then a flashing E02.

1. Unplug the ionization cable
2. Start SERV function 1
3. Wait for the start attempts to finish and E02 to flash
4. Reconnect the cable and reset the boiler

Read the technical read-out and error history

Rinnai · E50CRN; E75CRN; E75CRP; E110CRN; E110CRP

Hold STEP 5 s to switch the display to the technical read-out (status digit left, supply temperature / water pressure right). The ERRO chapter stores the last error (Err.L) and five earlier ones (Err.1 to Err.5) with status, T1, T2, kW and pump %.

1. Hold STEP 5 s to toggle the technical read-out
2. For history: enter C123, press MODE until ERRO, STEP through Err.L to Err.5

Actuator test: drive fan, burner, pump and 3-way valve by hand

Viessmann · Vitodens 200-W B2HE 85, 120, 150, 199

Each actuator test function runs for 30 s: fan rpm, burner Off / Min / Max heating / Max DHW, 3-way valve Heating / Centre / DHW, pump speeds, mixers, zone pumps.

1. Service menu > Actuator test
2. Pick the group (Boiler, Heating, DHW, Solar) and the function
3. Function stays active 30 s, then drops out