FC19 Intermittent Fault – Reset Using Spectrolink Controller (THM / THM5 / THM6)

⚠️ Safety Notice – Gas Heating Products

This appliance must only be installed, commissioned, serviced and repaired by suitably qualified and licensed personnel.

Before commencing work, complete a task-specific risk assessment and ensure gas and electrical safety requirements, ventilation provisions, safe access, adequate service clearances and appropriate PPE have been considered. All work must comply with applicable regulations, standards and manufacturer requirements.

Particular care must be taken when working around gas systems, electrical components, combustion products, hot surfaces, moving parts, roof spaces, ceiling spaces and confined spaces.

Do not proceed if safe access, required clearances, ventilation requirements, confined space risks or appropriate safety controls cannot be achieved and maintained. 

Safety takes priority over diagnosis, repairs, installation schedules and customer expectations. If the task cannot be completed safely, it must not proceed until the risks have been adequately controlled.

Fault Code FC19 – HX OT2 Open at Start

FC19 occurs when the heater detects that Heat Exchanger Over-Temperature Switch 2 (HX OT2 – 130°C) is open at start-up while HX OT1 remains closed.

When this condition is detected, the heater enters Lockout 2 and can only be reset through Service Mode using a Braemar Spectrolink Controller (SCC).

Important: HX OT2 is wired in the 24 V supply circuit to the gas valve. If the switch is open, the heater will not operate.

Possible Causes

• HX OT2 wiring disconnected or damaged.
• Power outage occurred while the heater was operating in heating mode, and power was restored before the over-temperature switches had cooled and reset.
• Faulty HX OT1 and/or HX OT2 switches.
• Restricted airflow caused by ductwork not meeting installation guidelines.
• Low airflow due to fan speed settings selected by the user.

Recommended Action

1. Check Wiring

Inspect the wiring to HX OT2 and reconnect if necessary.

2. Replace Both Over-Temperature Switches

If wiring is satisfactory:

• Replace HX OT1
• Replace HX OT2

Both switches should be replaced together, as a faulty HX OT1 can prevent the fault from being detected correctly.

3. Verify Airflow

After replacing the switches:

• Confirm normal heater operation.
• Verify airflow rates are within specifications.
• Check for any ductwork restrictions.

Additional guidance on TG, TH and THM FC19 diagnostics Click link below to view: 

FC19 Fault Code – HX OT2 Opened Spectrolink Reset Procedure, FC10 History Check & Overheating Diagnosis (TG, TH, THM, THM5 & THM6): Seeley International Pty Ltd 

If FC19 Continues to Occur

If FC19 remains intermittent after replacing both switches and no airflow issues can be found, the cause may be a faulty Modulating Control Board (MCB).

Replacement MCB Part Numbers

Natural Gas (NG)

• 640365 – PCB Modulating Control Board (MCB)

LPG

• 643410 – PCB Modulating Control Board (MCB)

Additional Recommendation for Older Heaters

For heaters manufactured in 2012 or earlier (pre-serial number T12071732), replace:

• MCB (appropriate NG or LPG part number above)
• 641096 – Loom BSC to MCB

This has been shown to improve reliability on older units.

Resetting FC19 Using a Spectrolink Controller (SCC)

Once the fault has been repaired:

1. Turn the SCC OFF using the ON/OFF button.
2. Open the controller door.
3. Press and hold Zone 3 for 5 seconds to enter Service Mode.
4. Wait approximately 5 seconds until the latest fault code is displayed and RESET flashes.
5. Press and hold the small, recessed Door Button, then press RESET.
6. To clear stored fault codes, press and hold FAN for 5 seconds.
7. Close the controller door.
8. Press ON/OFF to return the heater to normal operation.

Technician Note

If FC19 occurs repeatedly with no obvious airflow restrictions and both over-temperature switches have been replaced, proceed with MCB diagnosis and replacement before pursuing further component changes. This is particularly relevant for older THM heaters where MCB and loom deterioration may contribute to intermittent faults.