Error F.83

Safety precautions:

Turn off the boiler using the on/off switch or the user controls. Isolate electrical power at the boiler isolator before removing any covers. Do not open or work on gas components or internal combustion parts unless you are a Gas Safe engineer. If you smell gas, evacuate, ventilate, shut off the gas supply at the meter/isolator if safe to do so and call the gas emergency number immediately.

Initial homeowner checks (safe, simple things you can do):

1) Check the boiler display for F.83 and note when it appeared and any other fault codes. Photograph for the engineer if needed.

2) Check the system pressure on the boiler gauge. If pressure is below about 1.0 bar (or the level recommended in your manual), the system may need repressurising. If you know how to use the filling loop, you can bring pressure to the normal working range (commonly 1.0–1.5 bar) and then close the taps. If you are unsure, stop and call an engineer.

3) Bleed radiators to remove trapped air. Air can reduce flow and prevent the return temperature rising.

4) Reset the boiler once after repressurising/bleeding to see if the fault clears (follow the boiler handbook for reset). If the code returns immediately or the boiler will not run, proceed to call a professional.

5) Look and feel for visible leaks around the boiler, pipework and radiators. Note any persistent pressure loss.

6) Listen for pump operation when the boiler runs—if the pump is silent or noisy and not circulating, that can cause low flow and trigger F.83.

If the fault persists after the safe homeowner checks, do not attempt internal repairs. The following are diagnostic and repair steps that should be carried out by a qualified Gas Safe engineer (included here so you know what they will check):

1) Verify flow and return temperatures with an IR thermometer or sensors while the boiler fires to confirm the expected temperature rise (delta-T). Compare measured values to manufacturer tolerances.

2) Inspect the NTC sensors (flow and return) and their plugs/connectors for corrosion, loose connections or incorrect positioning. On EcoTEC models these sensors are accessible behind the front panel; a competent engineer will remove the cover with power isolated.

3) Measure sensor resistance/voltage with a meter and compare to the specified values in the service manual. Replace faulty thermistors or swap flow/return sensors as a diagnostic to see if the fault follows the sensor.

4) Check wiring continuity between sensors and the PCB, and inspect the PCB input for damage or poor connectors. Repair or replace damaged wiring and connectors.

5) Confirm pump speed and flow rate are correct; check for blockages, seized impeller, or airlock in the pump/pipework. Re-prime or replace pump if required.

6) Inspect heat exchanger for blockages, scale build-up or internal leaks that could reduce heat transfer. Clean or replace as necessary.

7) Check gas valve operation and combustion/heat input—insufficient gas flow or a badly adjusted valve can prevent adequate heat rise. Only Gas Safe engineers should adjust or replace gas components.

8) If PCB faults are suspected, run diagnostic tests with service software or replace the PCB as needed.

Important notes and when to call a professional:

- If the simple homeowner steps (repressurise, bleed, reset) do not clear the fault, call a Gas Safe registered engineer. Most F.83 causes require safe access inside the boiler, electrical and gas work, or component replacement and should not be attempted by unqualified people.

- If you find a leak, persistent pressure loss, or the boiler will not fire at all, isolate the boiler and call an engineer immediately.

- Keep records: note the fault code, what you tried, the boiler model and serial, and take photos of the error display and any visible wiring or leaking areas—this helps the engineer diagnose faster.

Summary: Start with safe checks you can do yourself (pressure, bleeding, reset). If the fault remains, stop and get a Gas Safe engineer to diagnose and repair sensors, wiring, pump, heat exchanger or gas-related causes. F.83 is often a sensor or wiring issue but can mask more serious faults, so professional assessment is normally required.