Worcester Bosch 2950 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch 2950 fault code mean?
Fault code 2950 means the boiler attempted to light the burner but the control board received no confirmation that a stable flame was established. As a safety precaution, the boiler enters a blocking or lockout state to prevent unsafe operation. It is closely linked to code 2951: if flame loss occurs too frequently in a short period, the boiler escalates from the temporary 2950 blocking fault to a 2951 locking fault, which requires a manual reset before the boiler will attempt to fire again. In plain terms, 2950 is the first warning that ignition has failed; 2951 is the boiler saying it has failed too many times and will not retry on its own.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or contaminated flame/ionisation sensor Common
The ionisation sensor monitors the flame once ignition occurs. If it is coated in residue, has drifted out of position, or has developed an electrical fault, it cannot confirm a stable flame even when one is present. This is one of the most frequent triggers for a 2950 on Worcester Bosch appliances.
- Worn or damaged ignition electrode or lead Common
The ignition electrode generates the spark that lights the burner. A cracked ceramic body, eroded tip, or damaged connecting lead can produce a weak or absent spark, meaning the burner never ignites in the first place.
- Gas supply interruption or low gas pressure Common
If the gas pressure at the boiler drops below the required level — due to a partially closed isolation valve, a supplier outage, or undersized pipework — there is not enough gas to sustain a flame. Checking whether other gas appliances in the property are working normally is a quick first check any homeowner can do.
- Incorrect CO₂ or air-to-gas ratio Sometimes
If the combustion mix is not calibrated correctly the burner may briefly catch but fail to hold a stable flame long enough for the sensor to register it. This is a commissioning or service-related issue requiring an engineer with combustion analysis equipment.
- Blocked or partially obstructed flue Sometimes
A blocked flue prevents exhaust gases from escaping, which starves the burner of the air it needs and can extinguish the flame shortly after ignition. Birds' nests, debris, or a poorly sited terminal are typical culprits.
- Blocked or frozen condensate pipe Sometimes
A frozen or blocked condensate discharge pipe can cause the boiler to shut down and may also disrupt the flue path on certain models. During cold snaps this is worth ruling out early, as it is one of the few checks a homeowner can safely carry out.
- Faulty gas valve Rare
A gas valve that is not opening correctly — or opening inconsistently — will deliver insufficient gas to the burner, preventing a reliable flame. This is relatively uncommon but becomes more likely on older appliances or those that have not been serviced regularly.
- Burner or heat exchanger gasket failure Rare
Damaged seals around the burner or heat exchanger can allow the flame to be disrupted by air ingress, preventing the sensor from seeing a steady signal. An engineer will check and re-seal these during a strip-down inspection.
How to fix it
- Check that your gas supply is live DIY safe
See whether other gas appliances in your home — a gas hob, for example — are working normally. If nothing is working, contact your gas supplier, as there may be a network outage or a problem with your meter. Make sure the isolation valve on the gas supply pipe to the boiler is fully open (handle in line with the pipe).
- Check for a frozen condensate pipe DIY safe
If outdoor temperatures are at or below freezing, inspect the external section of the condensate discharge pipe (usually a white plastic pipe running through an outside wall) for ice. You can thaw it gently using a warm — not boiling — water bottle or a warm damp cloth wrapped around the pipe. Never use a naked flame or boiling water, as this can crack the pipework.
- Reset the boiler once DIY safe
Press and hold the reset button as described in your boiler's user guide. Allow the boiler to run through its full ignition sequence. If it fires successfully and runs normally, monitor it over the next day or two. If the fault returns, do not keep resetting — repeated lockouts indicate an underlying problem that needs professional attention.
- Do not attempt to open the boiler casing or touch internal components Gas Safe engineer
Any work inside the boiler — inspecting the electrodes, sensor, gas valve, fan, PCB, or burner — must only be carried out by a Gas Safe registered engineer. Opening the casing yourself is dangerous, may constitute illegal gas work, and is likely to invalidate your warranty or boiler cover.
- Have a Gas Safe engineer test the ignition electrode and lead Gas Safe engineer
The engineer will check the electrode for wear, cracks, or carbon fouling and measure the spark gap. The connecting lead will also be tested for continuity and insulation breakdown. Either component can be replaced individually if faulty, which is one of the more straightforward and cost-effective repairs.
- Have the flame/ionisation sensor inspected and cleaned or replaced Gas Safe engineer
The engineer will remove the sensor, assess its condition, and clean off any residue. If the sensor itself has failed electrically, it will be swapped for a new one. This is often the root cause on Worcester Bosch boilers showing a 2950.
- Have gas pressure tested at full load Gas Safe engineer
The engineer will measure the gas pressure at the boiler while it is firing at maximum output. If the pressure is low, they will trace whether the issue lies with the meter, the supply pipework, or the gas valve itself.
- Have combustion CO₂ settings checked and adjusted Gas Safe engineer
Using a flue gas analyser, the engineer will verify that the air-to-gas ratio is within the manufacturer's specified range. Incorrect settings are adjusted via the gas valve or air inlet — this is a Gas Safe task and should be part of every annual service.
- Have the flue and condensate routing inspected Gas Safe engineer
The engineer will check the entire flue run for obstructions and confirm that the condensate pipe falls correctly to its drain point. Any blockage or incorrect routing will be rectified.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the simple homeowner checks above have not resolved the issue, or if the boiler returns to fault shortly after reset, contact a Gas Safe registered engineer. You can verify an engineer's registration at gassaferegister.co.uk. Do not continue to operate a boiler that is repeatedly failing to establish a flame.
Parts you may need
- Ignition electrode · from £45
- Ignition lead / HT lead · from £25
- Flame/ionisation sensor · from £40
- Gas valve · from £120
- Burner gasket set · from £20
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£350, depending on the underlying cause.
Frequently asked questions
What is the difference between fault codes 2950 and 2951 on a Worcester Bosch boiler?
Code 2950 is a blocking fault — the boiler failed to detect a flame after one ignition attempt and has paused, but it may retry automatically. Code 2951 is a locking fault that appears when flame loss has occurred too frequently; the boiler will not attempt to fire again until it is manually reset. If you are seeing 2951 regularly, it means the underlying 2950 cause has not been resolved.
Can I reset a Worcester Bosch 2950 fault myself?
Yes, a single reset is a reasonable first step and is safe for a homeowner to do. Press and hold the reset button until the boiler attempts to ignite. If it starts and runs normally, keep an eye on it. However, if the fault returns after one or two resets, stop resetting and call a Gas Safe engineer — repeated resets without a fix do not address the cause and can mask a more serious problem.
How much does it typically cost to fix a Worcester Bosch 2950 fault in the UK?
Most people with this fault end up paying somewhere between £150 and £350, depending on what the engineer finds. Cleaning or replacing the ignition electrode or flame sensor sits at the lower end of that range. If the gas valve needs replacing the bill will be higher, typically £180–£250 including labour. Rare big-ticket repairs such as a PCB replacement can cost £300–£500 or more, but these are not the common outcome for a 2950. Labour rates are noticeably higher in London and the South East.
Is a Worcester Bosch 2950 fault dangerous?
The fault itself means the boiler has correctly detected a problem and shut down safely — that is the system working as intended. However, if you smell gas at any point, do not attempt to reset the boiler. Leave the property, avoid operating any electrical switches, and call the National Gas Emergency Service immediately on 0800 111 999. That number is free and available 24 hours a day.
Will an annual service help prevent fault code 2950?
Yes. The most common causes — a fouled ionisation sensor, a worn electrode, drifted CO₂ settings, and a deteriorating burner gasket — are all picked up and corrected during a properly conducted annual service. Worcester Bosch also recommend yearly servicing to keep the warranty valid, so it is worthwhile on both a safety and financial basis.