Buderus 3F 273 Fault Code: Causes, Fixes & Repair Costs
What does the Buderus 3F 273 fault code mean?
The 3F 273 code appears on Buderus boilers — most notably the Logamax Plus GB142 series — when the burner and fan have been running continuously for 24 hours without interruption. As a built-in safety measure, the boiler briefly suspends operation to carry out internal checks before resuming. Unlike a hard lockout code, this is classified as a blocking (non-locking) fault, meaning the boiler should restart automatically once the condition clears. However, if 3F 273 keeps returning, it is a strong signal that something is preventing the boiler from cycling normally, and an underlying fault needs investigating.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. 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
- Continuous heating demand from thermostat or controller Common
During an extended cold snap, or if a room thermostat or programmable controller has developed a fault and is sending a constant heat-demand signal, the boiler may genuinely run for 24 hours straight. The 3F 273 code then appears as the system carries out its routine safety pause. Check whether your thermostat or smart controller is set correctly and is cycling normally.
- Fan or blower fault Common
If the fan is not reaching its target speed — due to worn bearings, a build-up of debris on the impeller, or a damaged wiring harness — the boiler may struggle to complete ignition cycles cleanly, causing extended or repeated run attempts that accumulate toward the 24-hour threshold. A Gas Safe engineer can check fan speed and terminal voltage.
- Blocked or partially obstructed flue Common
A restriction in the flue or air supply — caused by debris, ice, a bird nesting, or soot build-up — reduces combustion efficiency and can prevent the boiler from satisfying demand efficiently, leading to prolonged run times. The flue and its terminal should be inspected.
- Blocked condensate or venturi tube Sometimes
On some GB142 variants, condensate can accumulate inside the venturi tube if it is not directed away properly. A partial blockage here disrupts the air-gas mixture, affecting combustion and potentially contributing to abnormal run behaviour. Removing and cleaning the venturi tube can resolve this.
- Faulty pressure switch (manostat) Sometimes
The manostat monitors air pressure in the combustion circuit. If it is sticking, reading incorrectly, or if its connecting tubes are partially blocked, the boiler may not confirm that airflow conditions are correct, leading to extended operation attempts. An engineer can test the switch and blow out its tubes.
- Electrical supply issues or parasitic voltage Sometimes
Voltage fluctuations, power supply interruptions, or stray voltages on the boiler casing (sometimes caused by nearby high-power appliances or damaged cable insulation) can interfere with the control board and produce unexpected fault behaviour including 3F 273. Checking mains polarity and supply quality may help.
- PCB or control board failure Rare
If the control board is malfunctioning, it may misread sensor inputs or fail to manage the burner cycle correctly, which can manifest as the 3F 273 code. This is typically suspected only after other causes have been ruled out.
How to fix it
- Check that your thermostat and heating controls are set correctly DIY safe
Verify that your room thermostat, programmer, or smart controller is set to a sensible temperature and is cycling on and off normally. A thermostat stuck in the 'on' position will keep requesting heat indefinitely. If you have a smart thermostat, check its app or settings for any unusual schedules.
- Wait for the automatic restart DIY safe
Because 3F 273 is a blocking rather than a locking fault, the boiler is designed to resume operation automatically after its internal safety pause. Give it 10–15 minutes before intervening further. If it restarts and runs normally, monitor it over the next 24 hours to see whether the code returns.
- Reset the boiler — but no more than twice or three times DIY safe
If the boiler has not restarted automatically after 15 minutes, press and hold the reset button for 2–3 seconds as described in your user guide. Do not reset more than two or three times in succession: repeated resets without a successful ignition can damage the ignition transformer. If the fault reappears immediately after resetting, stop and call an engineer.
- Check your system pressure DIY safe
Look at the pressure gauge on the boiler. It should read between 1.0 and 1.5 bar when cold. If it is below 0.8 bar, top it up via the filling loop following the instructions in your boiler manual. Low pressure can cause extended or abnormal operation.
- Inspect the flue terminal for obvious blockages DIY safe
Go outside and check the flue outlet (usually on an external wall or the roof) for any visible obstruction such as ice, debris, or a bird nest blocking the terminal. Do not attempt to work at height unsafely. If you spot a blockage you cannot safely clear, report it to an engineer.
- Check and thaw the condensate pipe if frozen DIY safe
In cold weather, the external condensate pipe can freeze and cause the boiler to behave abnormally. If it feels solid, gently pour warm (not boiling) water along the pipe or apply a warm cloth until it thaws. Once clear, attempt a reset.
- Have a Gas Safe engineer inspect the fan and venturi tube Gas Safe engineer
An engineer should check that the fan impeller spins freely, measure the voltage at the fan terminals, and inspect the wiring harness for damage. They should also remove and clean the venturi tube to clear any moisture or debris. These tasks involve internal boiler components and must not be attempted by a homeowner.
- Have a Gas Safe engineer test the pressure switch (manostat) Gas Safe engineer
The engineer can blow out the manostat's connecting tubes, listen for the characteristic click that confirms the switch is working, and replace the unit if it fails the test. This is an internal combustion-circuit component and requires Gas Safe competence.
- Have a Gas Safe engineer check the flue system internally and clean if needed Gas Safe engineer
A thorough flue inspection — including soot removal and checking for correct draw — should be carried out by a qualified engineer. Restricted flues are both a performance and a carbon monoxide safety issue.
- Have a Gas Safe engineer inspect the PCB and electrical supply quality Gas Safe engineer
If all other causes have been excluded, an engineer should inspect the control board for signs of heat damage, corrosion, or condensation, and check mains polarity and supply voltage. PCB replacement, if needed, must be configured correctly for the specific boiler model.
- Call a Gas Safe registered engineer Gas Safe engineer
If the 3F 273 code keeps returning after basic homeowner checks, or if the boiler is not restarting automatically, contact a Gas Safe registered engineer. Provide them with the full fault code (3F 273) and your boiler model (e.g. Logamax Plus GB142-30) so they can prepare before arriving.
Parts you may need
- Boiler fan / blower assembly (GB142-compatible) · from £120
- Pressure switch (manostat) · from £45
- Venturi tube / air-gas mixing tube · from £35
- PCB / main control board · from £280
- Flue terminal and pipe sections · from £40
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 £120–£380, depending on the underlying cause.
Frequently asked questions
Will the Buderus 3F 273 fault clear itself, or do I need to reset the boiler?
In most cases it should clear on its own. The 3F 273 is a blocking fault rather than a hard lockout, so the boiler is designed to resume automatically after a brief safety pause. If it has not restarted within 15 minutes, try a single reset using the button on the boiler. If the code comes back immediately or repeatedly, there is an underlying fault that needs a Gas Safe engineer to investigate.
Why does my Buderus boiler keep showing 3F 273 every day?
If the code is recurring daily, the boiler is almost certainly running for very long periods without satisfying the heating demand. The most common reasons are a thermostat or controller that is not cycling correctly (stuck calling for heat), a fan that is struggling to reach its target speed, or a partially blocked flue reducing combustion efficiency. An engineer can run a diagnostic to identify which component is responsible.
How much does it cost to fix a Buderus 3F 273 fault in the UK?
It depends on the root cause. A fan clean or pressure-switch replacement typically costs between £120 and £250 including labour. Fan replacement usually falls in the £200–£350 range. If the fault turns out to be a PCB failure, the cost can rise to £450–£700 or more for parts and labour, though this is less common. Most people with a recurring 3F 273 fault pay somewhere in the £120–£380 range once the actual cause is found and fixed.
Is the Buderus 3F 273 code dangerous — could it indicate a carbon monoxide risk?
The code itself indicates a 24-hour continuous run rather than a combustion safety trip, so it is not a direct carbon monoxide warning. However, some of its underlying causes — such as a restricted flue or poor combustion — can pose a CO risk if left unaddressed. Ensure you have a working, in-date carbon monoxide alarm in the same room as the boiler, and have the flue checked by a Gas Safe engineer if you suspect any blockage.