Viessmann EB Fault Code: No Flame Signal During Calibration
The EB fault code on a Viessmann boiler indicates that the boiler failed to detect a valid flame signal during its ignition calibration sequence at startup. When the boiler fires up, it runs a brief calibration routine to confirm the burner has lit correctly. If no flame is detected during this window, the boiler shuts down as a safety measure and displays EB. This is subtly different from a general ignition lockout — the failure occurs specifically within the calibration phase, pointing the finger at the flame detection system, the ignition components, or the gas supply reaching the burner.
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.
What does the Viessmann EB fault code mean?
The EB fault code on a Viessmann boiler indicates that the boiler failed to detect a valid flame signal during its ignition calibration sequence at startup. When the boiler fires up, it runs a brief calibration routine to confirm the burner has lit correctly. If no flame is detected during this window, the boiler shuts down as a safety measure and displays EB. This is subtly different from a general ignition lockout — the failure occurs specifically within the calibration phase, pointing the finger at the flame detection system, the ignition components, or the gas supply reaching the burner.
Common causes
- Dirty or degraded ionisation probe (flame sensor) Common
The ionisation probe sits inside the combustion chamber and monitors the burner flame by detecting a tiny electrical current through the flame. Carbon deposits and combustion residue build up on its surface over time, insulating it and preventing a reliable signal from being generated during the calibration phase. This is the single most common trigger for the EB code and is often resolved by cleaning or replacing the probe.
- Ignition electrode failure or wear Common
If the ignition electrode is cracked, heavily worn, or has an incorrect spark gap, the burner may fail to light at all during calibration. Even a weak or intermittent spark can mean the flame never fully establishes, leaving the flame sensor with nothing to detect.
- Low or interrupted gas supply to the boiler Common
If gas pressure at the boiler is below the required operating range, the burner cannot sustain a stable flame. This may be caused by a partly closed isolation valve, a problem with the meter, or supplier-side pressure issues. Checking whether other gas appliances in your home are working normally is a quick first indicator.
- Fan not at standstill or unstable fan connection Sometimes
Viessmann boilers check that the flue fan has fully stopped before initiating a new ignition sequence. If the fan is still spinning from a previous cycle, or if its plug-in wiring connection is loose, the boiler will enter burner fault mode and display EB rather than attempting to fire.
- Blocked burner or contaminated combustion chamber Sometimes
Debris, dust, or combustion residue in the burner head or chamber can disrupt the air-to-gas mixture needed for a clean, detectable flame. A partial blockage may allow the boiler to attempt ignition but not produce a flame strong enough for the sensor to register during calibration.
- Overheating or temperature sensor fault Sometimes
If a temperature sensor is reading incorrectly or the boiler has been running at excessively high setpoints, safety mechanisms can prevent the burner from firing. A faulty sensor may report false overheating conditions, triggering a lockout before the calibration sequence completes.
- Wiring fault or corrosion on burner connections Sometimes
Damaged, loose, or corroded wiring between the flame sensor, ignition electrode, and the boiler's control board can interrupt the signal path. The calibration routine may fail simply because the sensor's output cannot reach the PCB reliably, even if the component itself is functioning.
- PCB (printed circuit board) failure Rare
If the control board is faulty, it may misinterpret or fail to receive the flame signal even when the burner is lighting correctly. PCB failure is relatively rare but tends to be suspected only after all other components have been checked and found to be in good order.
- Circulating pump failure (certain models) Rare
On some Viessmann models including the Vitocrossal 200, a seized or failing pump can cause the boiler to overheat rapidly after firing, triggering a safety lockout that presents as a burner fault. The burner is not necessarily at fault — it is the lack of water circulation that causes the shutdown.
How to fix it
- Reset the boiler — but no more than twice DIY safe
Locate the reset button on your Viessmann boiler (usually marked with a flame symbol or labelled 'Reset'). Press and hold it briefly until the boiler attempts to restart. Viessmann allows up to three resets within a 24-hour window before enforcing a deeper safety lockout. If the EB code returns after one or two resets, do not keep trying — repeated unsuccessful resets accelerate wear on ignition components and will not fix an underlying fault.
- Check your gas supply is active DIY safe
Try another gas appliance in your home — a gas hob or gas fire — to confirm the supply is live. If other appliances are also not working, contact your gas supplier. Check that the isolation valve on the gas pipe leading to the boiler is fully open (handle parallel to the pipe). Do not attempt to adjust or test the gas valve on the boiler itself.
- Check the condensate pipe for a freeze or blockage DIY safe
In cold weather, the condensate pipe — the white plastic pipe that runs from the boiler to an external drain — can freeze solid, causing a lockout. If it feels solid or you can hear the boiler struggling, you can carefully pour warm (not boiling) water over the external section of the pipe to thaw it, then reset the boiler. If the pipe is not frozen, check it is draining freely and is not kinked or blocked.
- Check system pressure is within the correct range DIY safe
Look at the pressure gauge on the boiler. Most Viessmann models should show between 1.0 and 1.5 bar when cold. If it is below 0.8 bar, the system may need topping up via the filling loop. Refer to your boiler manual for the correct procedure for your model. If pressure is too high (above 2.5 bar) or keeps dropping, an engineer should investigate.
- Have a Gas Safe engineer inspect and clean the ionisation probe Gas Safe engineer
An engineer will access the combustion chamber, remove the ionisation probe, and assess whether carbon deposits are responsible for the signal failure. In many cases a thorough clean restores normal operation. If the probe is damaged or degraded, it will be replaced. The engineer will also test its electrical output with a multimeter to confirm it is reading correctly after the service.
- Have the ignition electrode inspected and tested Gas Safe engineer
The engineer will check the electrode for cracking, erosion, and correct positioning. They will also verify the spark gap is within specification. A weak or absent spark during the calibration window is a common contributor to the EB code and the electrode is a relatively low-cost part to replace if needed.
- Have gas pressure checked at the gas valve Gas Safe engineer
The engineer will measure static and working gas pressure at the boiler's gas valve using appropriate test equipment to confirm the boiler is receiving gas at the correct pressure for your fuel type. If pressure is out of range, this will need to be investigated upstream by a qualified professional.
- Have the fan and its connections inspected Gas Safe engineer
The engineer will confirm the fan comes to a complete standstill between cycles and that its wiring connector is secure and undamaged. A fan that coasts too long or has a loose connection can prevent the boiler from initiating its ignition sequence correctly.
- Have the burner and combustion chamber cleaned and assessed Gas Safe engineer
The engineer will inspect the burner head for blockages or contamination that could be disrupting the air-gas mixture. On models with a stainless steel Inox-Radial heat exchanger, a full combustion analysis — including ionisation readings and burner gasket inspection — is required rather than a visual check alone. This is also necessary to maintain any extended Viessmann warranty.
- Have the PCB tested if all other components are in order Gas Safe engineer
If the ionisation probe, ignition electrode, gas supply, fan, and burner have all been checked and found to be working correctly, the engineer will test the control board. The PCB is responsible for interpreting the sensor signals and managing the calibration sequence, and a fault here can produce an EB code even when the hardware is functioning. PCB replacement is a significant cost and is usually the last avenue explored.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
If the boiler has not cleared after basic homeowner checks, or if it keeps returning to the EB fault, you need a Gas Safe registered engineer to diagnose and repair the fault safely. Do not attempt to access internal gas components, the combustion chamber, or any wiring yourself. You can verify an engineer's Gas Safe registration at gassaferegister.co.uk.
Parts you may need
- Ionisation probe (flame sensor) · from £35
- Ignition electrode · from £25
- Flue fan assembly · from £180
- Circulating pump · from £120
- Gas valve · from £150
- PCB (control board) · from £280
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 £90–£380, depending on the underlying cause.
Frequently asked questions
Is the Viessmann EB code the same as the EE code?
They are closely related but not identical. The EE code is a general 'no flame signal' lockout that can occur at any point during boiler operation. The EB code is more specific — it means no flame was detected during the ignition calibration sequence that runs at startup. In practice, many of the same components are involved (ionisation probe, ignition electrode, gas supply), but EB points more directly at the calibration phase and the flame detection system during that window.
Can I reset a Viessmann EB fault myself?
Yes, you can attempt a reset — but only up to twice in quick succession. If the EB code clears and the boiler runs normally, monitor it over the next day or so. If it returns, or if the boiler fails to start after two resets, stop resetting and call a Gas Safe engineer. Repeated resets without fixing the root cause put extra stress on the ignition components and will not resolve a genuine fault.
How much does it typically cost to fix a Viessmann EB fault code in the UK?
Most EB fault repairs fall in the range of £90 to £380 including parts and labour. Cleaning or replacing the ionisation probe tends to be at the lower end, while fan or pump replacements sit in the middle. If the PCB or heat exchanger turns out to be the cause, costs can climb significantly higher — PCB replacement on a Viessmann boiler can reach £400 to £600 once labour is included. An engineer's diagnostic visit is usually £70 to £100 on its own.
Will fixing an EB fault affect my Viessmann warranty?
Viessmann extended warranties (which can cover 10 to 12 years on certain models) require annual servicing by a Gas Safe registered engineer to remain valid. If your boiler has not been serviced regularly and you now have a fault, your warranty protection may be reduced or voided. Any repair work carried out also needs to be done by a qualified professional. If your boiler is still within its warranty period, contact Viessmann directly before arranging an independent engineer, as the repair may be covered.