Error 2948 B

Safety first

- If you smell gas, evacuate everyone from the property immediately, do not operate electrical switches or the boiler, call the national gas emergency number (or local emergency services) and your gas supplier. Do not attempt any repairs.

- If you are not confident working around gas or electrics, stop and call a Gas Safe registered engineer. Internal burner, electrode or gas-valve work must only be done by a qualified engineer.

- Before attempting any checks, switch the boiler off and isolate electrical power at the fused spur, unless a step explicitly requires the boiler to be powered on (in which case only visual checks are advised).

Initial homeowner checks (safe, simple checks)

1. Note the fault and any cause code shown on the display. Take a photo if helpful for the engineer.

2. Try a reset: follow the boiler manual reset procedure (usually hold the reset button for ~3 seconds or the reset position on the control dial). Wait and observe. If the boiler restarts and runs normally for a reasonable period, monitor it — one brief fault can be transient. Do not keep resetting repeatedly.

3. Check the property gas supply: confirm other gas appliances (hob, gas fire) work normally. Check the gas meter isolation valve (do not tamper with meter internals). If there is no gas supply to the property, contact your gas supplier.

4. Check the boiler display and LEDs: some Greenstar models flash a blue light with flame-related faults — note any pattern and include it when you contact a technician.

5. Check for obvious blockages or damage to the flue terminal and air intake outside (leaves, nests). Ensure ventilation around the boiler is not obstructed. Also check condensate pipe externally in cold weather for freezing or blockage.

6. If the boiler was recently serviced or cleaned and the fault first appeared afterward, note what work was done — moisture or incorrect reassembly can cause ignition/flame sensing issues.

Specific diagnostic steps a homeowner can safely perform (visual, non-invasive)

1. With the boiler powered off, visually inspect for obvious loose connections to the control PCB or terminal strips that are externally accessible (do not remove covers or probes). If you see a disconnected wire you are not sure about, stop and call an engineer.

2. Look for signs of water or corrosion inside any visible grille or inspection window at the burner/flue area (do not insert tools). Moisture on the electrode can prevent ionisation.

3. If the boiler has been in minimum/siphon fill mode after a long off period or after the control knob has been turned down and back up, allow 15–30 minutes; this is normal behaviour and may clear itself. If the symbol or minimum operation continues beyond 30 minutes, get an engineer.

When to call a professional (and what they will check)

- Call a Gas Safe registered engineer if: the fault remains after a reset; the fault recurs; there is any smell of gas; you are not confident with the above checks; or the boiler has been opened by anyone unqualified.

- The engineer will run safe diagnostics: check and measure gas pressure and gas valve operation, inspect and test the ignition electrode and ionisation/flame sensor and replace if necessary, examine the high-tension lead and connectors, check the CO2/gas valve settings and leak tests where applicable, inspect the PCB/ignition module and flame detection circuit, check the fan and flue for proper operation and test combustion where required. They will also clear cause codes, confirm burner low/high settings, and perform a full safety and commissioning check.

Other important notes

- Do not attempt to adjust or replace the gas valve, electrode assembly, or PCB yourself. These are gas work/electrical items requiring qualification and correct commissioning. Repeatedly resetting the boiler without fixing the underlying cause is not safe and can mask a dangerous condition.

- If the fault only appears briefly after cleaning or after a Service and then clears, mention this to the engineer — it may indicate electrode contamination, incorrect reassembly, or a need for electrode replacement or gas-valve calibration.

- Always use a Gas Safe registered engineer for repairs or checks involving gas components, combustion testing, or PCB/ignition module replacement. Provide the engineer with the exact fault code (2948 B) and any cause code or display behaviour you recorded to speed diagnosis.