Viessmann 19 Fault Code: Causes, Fixes & Repair Costs
What does the Viessmann 19 fault code mean?
Fault code 19 on Viessmann boilers indicates that the burner control unit has detected a problem with the fan — specifically that the fan has not reached a standstill when expected, is running at an incorrect RPM, or has an unstable plug-in connection. As a safety measure, the boiler locks out and refuses to fire until the fan issue is resolved. This is because the fan is responsible for safely expelling combustion gases from your home; if it cannot be confirmed to be working correctly, the boiler will not operate. This fault applies across the Viessmann range, including popular Vitodens models.
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 not spinning down to standstill Common
After each heating cycle the boiler's burner control unit expects the fan to wind down completely before allowing a new start. If the fan lingers at speed — due to a worn motor, bearing failure, or a stuck impeller — the control unit logs fault code 19 and locks out. This is the single most common trigger for this code.
- Loose or damaged plug-in wiring connector Common
The fan motor communicates its speed via a wiring loom with a push-fit connector. Vibration over time can loosen this connector, causing intermittent or incorrect RPM signals that the control unit interprets as a fan fault. Corroded or heat-damaged pins can produce the same effect.
- Faulty fan motor Sometimes
A fan motor that is mechanically worn, has burnt-out windings, or has seized bearings will either run at the wrong speed or fail to respond correctly to the control unit's commands. Because the boiler cannot verify safe flue-gas extraction, it locks out.
- Blocked or restricted flue terminal Sometimes
A partial blockage at the flue terminal — caused by a bird nest, ice build-up in cold weather, or accumulated debris — creates back-pressure that forces the fan to work harder. The resulting deviation from the expected RPM range can trigger code 19 even when the fan motor itself is in good condition.
- PCB fault Rare
The printed circuit board governs the fan speed control signal. A failing PCB may send incorrect voltage or frequency to the fan, or misread the tachometer feedback signal, causing a spurious fan fault to be logged. This is less common but should be considered if the fan and wiring check out as healthy.
How to fix it
- Check for an obvious flue blockage from outside DIY safe
Go outside and visually inspect the flue terminal. Look for a bird nest, ice cap, debris, or anything physically obstructing the outlet or inlet. Do not touch any gas pipework — just observe. If you spot a blockage that can be safely cleared without climbing ladders or accessing the roof, remove it. In winter, ice on a balanced flue terminal is a common cause of fan-related faults.
- Reset the boiler once DIY safe
On most Vitodens models, press and hold the Reset (R) button on the front panel for approximately two seconds until the boiler attempts to restart. On touchscreen models, follow the on-screen reset prompt. Allow the boiler a full start-up attempt. If it fires successfully and runs without returning the fault, monitor it over the next day or two. Do not reset more than two or three times in total — repeated resets without resolution can stress ignition components.
- Do not attempt to open the boiler casing or touch wiring yourself Gas Safe engineer
Although a loose fan connector is a common cause, accessing it requires removing the boiler casing and working around live electrical components and gas pipework. This must only be done by a Gas Safe registered engineer. Attempting this yourself is unsafe and will void any remaining warranty.
- Arrange a visit from a Gas Safe registered engineer for fan and wiring inspection Gas Safe engineer
An engineer will remove the casing, inspect the fan motor visually, check the plug-in connector for security and corrosion, and test the fan's actual RPM against Viessmann's specification for your model. They will also verify that the flue system is clear and that back-pressure is not causing the fan to run outside its expected speed range.
- Fan motor testing and replacement if required Gas Safe engineer
If the motor fails the RPM or electrical test, the engineer will replace it with a compatible Viessmann fan assembly. Fan components are model-specific, so it is important the engineer sources the correct part. A Viessmann-trained installer will have direct access to genuine parts and diagnostic tools.
- PCB inspection and testing Gas Safe engineer
Should the fan and wiring prove to be in good condition, the engineer will turn their attention to the PCB — testing the fan control output and the tachometer input circuit. A faulty PCB will need to be replaced by a qualified engineer and should never be handled by a homeowner.
Parts you may need
- Viessmann fan motor assembly (model-specific) · from £120
- Fan wiring loom / plug connector · from £25
- PCB (burner control unit) · from £180
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
Is fault code 19 dangerous — should I keep using the boiler?
No, you should not attempt to override or repeatedly reset the boiler to keep it running. Code 19 is a safety lockout: the boiler has detected that it cannot confirm safe flue-gas extraction. Running the boiler in this state carries a risk of incomplete combustion products, including carbon monoxide, entering your home. Leave it locked out and call a Gas Safe registered engineer promptly.
How much does it cost to fix Viessmann fault code 19?
For the most common fix — fan motor replacement including parts and labour — most UK homeowners pay between £150 and £400 depending on the model and their location. A diagnostic call-out alone is typically £80–£130. If the PCB turns out to be at fault, costs can rise further, sometimes to £500 or more for a genuine Viessmann board plus labour. In rare cases where the boiler is old and beyond economical repair, full replacement becomes the more cost-effective route.
Can I fix fault code 19 myself?
There is very little a homeowner can safely do beyond a visual check of the flue terminal for obvious blockages and a single boiler reset. The fan, its wiring, and the PCB are all inside the boiler casing, and working on them requires a Gas Safe registered engineer. Attempting DIY repairs on these components is unsafe and will invalidate your Viessmann warranty.
Will my Viessmann warranty cover a fault code 19 repair?
Viessmann's extended warranty (where applicable) does cover component failures such as a faulty fan motor, provided the boiler has had its annual service carried out by a Gas Safe registered engineer — ideally a Viessmann-approved installer. If annual servicing has been skipped, Viessmann can void warranty cover, leaving you to meet the full repair cost. Always keep your service records as proof.