Viessmann 30 Fault Code: Causes, Fixes & Repair Costs
What does the Viessmann 30 fault code mean?
Fault code 30 on Viessmann boilers signals that the burner control unit has entered a safety lockout because the fan has failed to come to a complete stop after a heating cycle, or because an unstable electrical connection to the fan has been detected. When the boiler finishes a cycle, the control unit expects the fan to idle down and halt within a defined window. If it keeps spinning — or if the fan speed signal received by the control board looks wrong — the boiler interprets this as a potential flue-gas hazard and locks out to protect the household. A secondary trigger for the same code is a loose or intermittent plug-in connection between the fan and the PCB, which can cause the controller to misread fan status entirely.
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 motor not stopping after shutdown Common
The most frequent trigger for code 30. Once a heating demand ends, the fan should wind down and stop within a set period. A worn motor, a stuck bearing, or a failing motor capacitor can prevent this, leaving the fan still turning when the control unit polls for a standstill condition. The boiler immediately locks out as a flue-safety measure.
- Faulty or failing fan motor Common
As fan motors age, their internal bearings wear and winding insulation can degrade. This causes erratic RPM behaviour — the motor may spin too fast, too slowly, or refuse to stop on command. Because repair labour costs are comparable to replacement costs, engineers usually recommend a full fan unit swap rather than attempting a motor-only repair.
- Loose or damaged fan wiring and plug-in connection Sometimes
The fan communicates its speed via a signal cable and plug-in connector to the PCB. If this connector is corroded, partially seated, or has developed a broken wire, the PCB receives an unreliable or absent signal and codes fault 30 even when the fan itself is physically healthy. Vibration over time is a common cause of connector loosening.
- PCB misreading the fan speed signal Rare
In some cases the fan and its wiring are in good condition but the PCB's fan-monitoring circuit is faulty, causing it to report incorrect RPM values. This is less common and usually only considered once the fan and wiring have been ruled out. Viessmann covers PCB defects under the boiler warranty, so checking warranty status is worthwhile before authorising a replacement.
How to fix it
- Check whether the boiler is under warranty DIY safe
Viessmann boilers come with a manufacturer's warranty that typically covers component defects including the fan and PCB. If your boiler is still within its warranty period, contact Viessmann UK customer services on 01952 675000 before arranging an independent engineer visit, as the repair may be carried out at no cost to you.
- Attempt a single boiler reset DIY safe
Locate the reset button on your boiler's control panel (marked 'R' on many Vitodens models, or a flame symbol with a line through it). Press and hold it until the boiler attempts to restart. If the boiler fires up and runs normally, monitor it closely. Do not reset more than two or three times — repeated resets without an underlying fix can mask a developing fault and are not a cure for code 30.
- Do not attempt to open the boiler casing Gas Safe engineer
All internal inspection and repair work on the fan, wiring, and PCB must be carried out by a Gas Safe registered engineer. Opening the casing yourself is unsafe, will almost certainly void your warranty, and may leave the flue system in an unknown state.
- Engineer: inspect the fan and plug-in connections Gas Safe engineer
A Gas Safe engineer will remove the casing and visually inspect the fan assembly, checking for signs of bearing wear, motor damage, or overheating. All plug-in connectors and the fan signal cable will be reseated or replaced as needed. The engineer will also check for any blockage in the flue or air intake that could be contributing to abnormal fan behaviour.
- Engineer: test fan RPM and control signals Gas Safe engineer
Using diagnostic equipment or the boiler's own service mode, the engineer will run the fan and measure actual RPM against the values the PCB expects to see. This confirms whether the fault lies with the motor itself, the speed-sensing circuit, or the PCB's interpretation of that signal.
- Engineer: replace the fan if defective Gas Safe engineer
If the fan motor is confirmed faulty, a full fan unit replacement is the standard course of action. The engineer will source a Viessmann-compatible fan for the specific model, fit it, and verify that the boiler completes a full cycle — including a clean shutdown with the fan reaching standstill — before signing off the repair.
- Engineer: inspect and replace the PCB if required Gas Safe engineer
If the fan and all wiring test as healthy but fault 30 persists, the PCB's fan-monitoring circuitry is the likely culprit. PCB replacement is a specialist task and, if the boiler is within warranty, should be raised with Viessmann directly rather than sourcing a third-party board.
- Book an annual service to prevent recurrence DIY safe
An annual service by a Gas Safe engineer keeps fan bearings, electrical connections, and flue integrity in check before they deteriorate to the point of triggering a lockout. It is the single most effective preventative step for avoiding fault 30 in the future.
Parts you may need
- Viessmann boiler fan assembly (model-specific) · from £110
- Fan signal cable and connector set · from £18
- PCB (printed circuit board, 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 £200–£320, depending on the underlying cause.
Frequently asked questions
Can I fix Viessmann fault code 30 myself?
No. The fault relates to the boiler's fan and internal electrical connections, both of which sit inside the boiler casing. Working inside a boiler requires Gas Safe registration — doing so without it is illegal, dangerous, and will void your warranty. The only homeowner actions you can safely take are checking your warranty status, attempting one or two resets, and then calling a Gas Safe registered engineer.
How much does it cost to fix fault code 30 on a Viessmann boiler in the UK?
For most households the repair is a fan replacement, which typically costs £200–£320 including parts and labour. If the fault turns out to be a loose wiring connector, the engineer's call-out and diagnostic fee of £80–£120 may be the only charge. In rarer cases where the PCB needs replacing, costs can rise to £400–£550 — worth bearing in mind on older boilers where a service plan or replacement might make more financial sense.
Is fault code 30 covered under my Viessmann warranty?
Fan motor faults and PCB defects are generally covered under the Viessmann manufacturer's warranty. If your boiler is within its warranty period, contact Viessmann UK on 01952 675000 before arranging an independent engineer, as you may be entitled to a free repair or replacement component. Always check your warranty documentation for the exact terms and conditions, as third-party repairs carried out without Viessmann's knowledge can sometimes affect warranty validity.
Why does my Viessmann boiler keep showing fault code 30 even after a reset?
A reset clears the lockout temporarily but does nothing to address the underlying mechanical or electrical fault. If the fan motor is worn, a bearing is sticking, or a connector is loose, the boiler will simply detect the same problem again and re-enter lockout — sometimes within minutes or hours. Repeated resets without a proper repair risk damaging other components. If code 30 keeps returning, stop resetting and arrange an engineer visit promptly.