Viessmann bE Fault Code: Causes, Fixes & Repair Costs
What does the Viessmann bE fault code mean?
The bE fault code appears on Viessmann boiler displays when the boiler's control board detects that the fan has not come to a complete standstill before or after a firing cycle, or that an electrical plug-in connection associated with the fan circuit is unstable. Before every ignition attempt, the boiler's PCB runs a pre-ignition check to confirm the fan is at rest. If the fan is still spinning unexpectedly, spinning at the wrong speed, or if the connection carrying that status signal is intermittent, the boiler switches into lockout and shows bE. Note on the display: Viessmann uses a seven-segment LCD screen, so the code appears as 'bE' — the lowercase 'b' is simply how that segment arrangement renders the letter. Viessmann documentation may refer to the same code as 'BE'. It is one and the same fault.
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
- Fan fault — incorrect speed or failure to stop Common
The fan is the most frequent culprit. Once a heating cycle ends, the fan must spin down and come to a confirmed standstill before the PCB allows a fresh ignition sequence to begin. If the fan's bearings are worn, the motor is failing, or the speed sensor (tachometer) on the fan is giving incorrect readings, the PCB cannot confirm standstill and triggers the bE lockout. A fan that is mechanically seized or running too slowly will cause the same result.
- Loose or damaged plug-in connection to the fan Common
Vibration from normal boiler operation can cause the electrical connectors linking the fan to the wiring loom to work loose over time. Even a slightly intermittent contact is enough for the PCB to flag a connection error and lock out with bE. Corroded or heat-damaged connector pins produce identical symptoms.
- Air pressure switch fault or blocked condensate/flue path Sometimes
The air pressure switch monitors whether the fan is actually moving air. If the switch itself is faulty, or if the small rubber sensing tube between the fan housing and the switch is split, blocked, or waterlogged, the PCB receives contradictory signals about fan status. A partially blocked flue or condensate trap can also create back-pressure that confuses the switch reading.
- Faulty PCB Rare
If the fan, its wiring, and the air pressure switch all test within specification, the PCB itself may be misreading or failing to process the fan standstill signal correctly. PCB faults are relatively rare and are normally only confirmed after all other components have been ruled out by a qualified engineer with a multimeter.
How to fix it
- Check whether gas is on and no wider supply outage is affecting the property DIY safe
Before assuming a boiler fault, confirm the gas supply is live. Check that the isolation valve on the gas supply pipe to the boiler is open (handle in line with the pipe), and that other gas appliances in the home — such as a hob or gas fire — are working normally. If there is no gas at any appliance, contact your gas supplier.
- Visually inspect the fan wiring connectors (external visual only — do not open the boiler casing) DIY safe
With the boiler switched off at the mains, have a look at any visible wiring around the boiler. If a connector is clearly hanging loose where it exits the casing and is accessible without opening any panels, note this for the engineer. Do not remove boiler casing or touch internal components — this must be done by a Gas Safe registered engineer.
- Reset the boiler once or twice using the reset button or procedure in your user manual DIY safe
A bE lockout can occasionally be triggered by a transient electrical glitch. Press and hold the reset button (typically marked with a flame and cross symbol, or described in your Viessmann user manual) for around three seconds. Allow the boiler to complete its startup sequence. If the bE code returns within one or two attempts, stop resetting — repeated resets will not fix an underlying mechanical or electrical fault and may mask important diagnostic information.
- Engineer to inspect and test the fan, tachometer, and fan wiring harness Gas Safe engineer
A Gas Safe registered engineer will remove the boiler casing and use a multimeter to measure fan motor resistance, check the tachometer output signal, and verify that all connectors are fully seated and undamaged. If the fan is drawing incorrect current, delivering wrong speed signals, or the motor has failed, the engineer will replace the fan assembly.
- Engineer to test the air pressure switch and sensing tube Gas Safe engineer
The engineer will inspect the rubber sensing tube for splits, blockages, or water ingress, and test the air pressure switch contacts with a multimeter. If the switch is not opening and closing within its specified pressure range, or the sensing tube is compromised, the relevant component will be replaced. The condensate trap and flue termination will also be checked for obstructions.
- Engineer to assess the PCB if all other components test correctly Gas Safe engineer
Only once the fan, wiring, connectors, and air pressure switch have been confirmed serviceable should the PCB be considered as the fault source. The engineer will check for signs of burning, corrosion, or failed solder joints on the board. Given the cost of a PCB replacement (£400–£500 including labour), the engineer should also assess the overall condition and age of the boiler before recommending this repair over a boiler replacement.
- Call a Gas Safe registered engineer if the fault persists or you are unsure at any stage Gas Safe engineer
The bE code points to internal fan, wiring, or control components that require professional diagnosis. If the fault returns after a reset, or if you have not been able to identify a simple loose connection, contact a Gas Safe registered engineer. You can verify any engineer's registration at gassaferegister.co.uk. Viessmann also recommends using a Viessmann-trained installer for accurate diagnosis on their boilers.
Parts you may need
- Viessmann boiler fan assembly (model-specific) · from £120
- Air pressure switch · from £45
- Fan wiring harness / connector kit · from £25
- PCB (model-specific) · from £220
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–£400, depending on the underlying cause.
Frequently asked questions
Can I fix the Viessmann bE fault code myself?
Very little of this fault is safely DIY-accessible. As a homeowner you can check the gas supply is on, attempt one or two resets, and visually inspect visible external wiring — that is the extent of safe self-help. The fan, air pressure switch, wiring harness, and PCB are all internal components that require the boiler casing to be opened and components to be tested with specialist equipment. These checks must be carried out by a Gas Safe registered engineer.
How much does it cost to fix a Viessmann bE fault in the UK?
Most people with a bE fault pay somewhere between £150 and £400 all-in. A wiring or connector repair at the lower end, an air pressure switch replacement in the middle, and a fan replacement towards the top of that range. A PCB replacement is less common but typically costs £400–£500 including labour and parts — if your engineer suspects the PCB and the boiler is over ten years old, it is worth getting a new boiler quote at the same time, as modern condensing boilers can be more cost-effective than a high-value repair on an ageing unit.
Why does my Viessmann boiler keep showing bE even after I reset it?
A bE code that returns immediately or within a short time after resetting indicates that the underlying physical fault has not been resolved — the boiler's safety check is simply failing again at the same point in the startup sequence. Repeated resets will not cure a worn fan, a faulty air pressure switch, or a damaged connector. If the code keeps coming back, stop resetting and call a Gas Safe registered engineer to carry out a proper diagnosis with a multimeter.
Is the Viessmann bE code the same as the BE code?
Yes — they are the same fault. Viessmann boiler displays use a seven-segment LCD screen, and the way the segment characters are formed means the code appears as 'bE' (with a lowercase-style b). Viessmann's own technical documentation and some engineers may refer to it as 'BE'. Both refer to the same fan standstill and plug-in connection lockout condition.