Error NO CODE 212

Safety first

- If you smell gas: turn off the gas supply at the meter, do not operate electrical switches, ventilate the property and call the gas emergency service immediately. Do not attempt internal repairs.

- If there are signs of carbon monoxide (sickness, headaches, soot, yellow burner flame) switch off the boiler, leave the property and call emergency services and a Gas Safe engineer.

- Always isolate electrical supply to the boiler before removing the casing or touching mains wiring. If you are not qualified, do not open the boiler casing.

Initial quick checks a homeowner can do (safe, no internal access required)

1) Record exactly what the display/LEDs show and when the fault appeared (heating on, hot water only, after reset, after power cut). This info helps an engineer.

2) Try a single reset: press the boiler reset button once and observe. If the code returns immediately or after a short time, stop resetting and proceed with checks.

3) Check system water pressure on the boiler gauge. It should typically be around 1.0–1.5 bar when cold. If it’s low (below ~0.7–1.0 bar) repressurise following the manufacturer’s instructions and then try the reset again. If the system loses pressure again, there’s a leak or PRV fault and you need an engineer.

4) Check all radiator TRVs and lockshield valves are open and the thermostat/room stat calls for heat. A closed valve or fully shut system can create circulation restrictions.

5) Bleed radiators to remove any trapped air which can cause poor circulation and local temperature spikes.

6) Listen to the boiler when it tries to fire: can you hear the pump running? Do pipes warm gradually or does the flow pipe become very hot quickly? A totally silent pump or very rapid local heating can indicate a circulation failure or blockage.

7) Check for any visible leaks, condensation discharge from the PRV pipe (outside) or signs of overflow. If the PRV is discharging water, switch off and call an engineer.

8) Lower the central heating flow temperature (set the CH temperature lower via controls) as a temporary measure; slower rise reduces the chance of immediate trips and gives time to arrange a repair.

Further homeowner diagnostics (only if you are competent and safe to do so)

- With the boiler powered but before opening the casing, you can feel pipes (not touch internal components) to confirm whether the flow and return pipes are both changing temperature. If the flow gets very hot while the return stays cold, circulation is poor.

- Visually inspect any exposed sensor wiring and connectors for obvious damage or moisture. Do not disconnect live connectors or probe inside the boiler unless qualified.

When to stop and call a professional

- If the fault returns after a single reset, if you cannot restore normal operation with the simple checks above, or if you suspect a sensor, pump, valve, heat exchanger or control board issue, stop. DO NOT repeatedly reset the boiler — continual resets can mask a developing fault and are unsafe.

- Any internal component replacement, testing of NTC sensors, continuity checks, pump removal or control board work must be carried out by a Gas Safe registered engineer.

What a Gas Safe engineer will check and do

- Read the boiler fault log and run manufacturer diagnostics to determine whether the flow NTC, safety thermistor or wiring is at fault.

- Measure sensor resistances/temperatures with a multimeter, check sensor wiring/connectors for faults or moisture, and replace the flow/safety sensor or safety temperature limiter if defective.

- Test the pump for correct operation and flow rate; remove airlocks and, if necessary, service or replace the pump. Check and service the diverter valve if fitted.

- Inspect the heat exchanger for blockages or scale that could restrict flow and cause rapid local temperature rises; clean or replace as required.

- Check the control board and software for errors and verify the temperature-rise protection thresholds. Replace control electronics only if proven faulty.

- Pressure test the sealed system, check PRV operation and look for leaks.

Final notes

- Do not attempt internal repairs or component swaps unless you are Gas Safe qualified. Document fault behaviour and times to help the engineer diagnose the cause faster. If the fault is intermittent or happens under specific conditions (DHW vs CH, after power loss, only when radiators are cold), tell the engineer — those details greatly reduce diagnostic time.

- If you are unsure at any stage, or if the fault is persistent, arrange a visit from a Gas Safe registered Worcester Bosch-accredited engineer.