Viessmann Boiler Repairs
Experienced Viessmann Boiler Repairs specialists
Available 24 hours a day, 7 days a week
Insurance approved
All parts guaranteed for a year
Fully Gas Safe trained engineers
Viessmann Boiler Repairs London
Gas Safe registered engineers • 24/7 call handling • London wide
Call Now: 0203 868 6251
Tell us the fault code and model. We will advise the safest next step.
Common Viessmann models we repair include Vitodens 050-W, Vitodens 100-W, Vitodens 111-W, and Vitodens 200-W, with frequent calls for F4, F2, low pressure, and fan faults.
We fix Viessmann boiler fault codes, no heating, no hot water, lockout, leaking, and low pressure across London.
We also offer boiler servicing and boiler installation across London.
Quick Navigation
Safety First
Smell gas? Turn off the gas supply at the meter if it is safe to do so. Open windows. Leave the property. Call the National Gas Emergency Service on 0800 111 999. Do not use switches, and do not use naked flames.
CO alarm sounding? Open windows immediately. Leave the property. Call 999. Do not re-enter until cleared by emergency services.
Boiler leaking heavily? Turn off the boiler at the controls. If safe, turn off the water supply. Call an engineer.
Quick Checks Before You Call
Before calling an engineer, these safe checks may resolve simple issues with your Viessmann boiler.
Check the gas supply
Is gas working at other appliances in your home? If not, check your meter and any prepayment credit.
Check the pressure gauge
Pressure should read around 1.0 to 1.5 bar when cold. If below 1 bar, you may need to repressurise using the filling loop.
Check the thermostat
Is the room thermostat set above current room temperature? Are the batteries working?
Check the timer or programmer
Is the heating scheduled to be on? Check the clock is set correctly.
Try a single reset
Locate the reset button on your Viessmann boiler. Press once and wait. If the fault returns, do not keep resetting. Call an engineer.
Check the condensate pipe
In cold weather, the external condensate pipe can freeze. Look for a white plastic pipe exiting through an outside wall. If frozen, pour warm water over it gently.
Viessmann Fault Codes
Note: Viessmann fault codes can vary by model and controller. If your code is different, call us with the exact code and model and we will advise the safest next step.
Common Viessmann fault codes and what to do
| Code |
What It Means |
What To Do |
| F4 |
Ignition failure / no flame detected |
Check gas supply and whether other gas appliances work. Check condensate pipe in freezing weather. If it returns, call an engineer. |
| F2 |
Overheat protection triggered |
Do not keep resetting. Call an engineer to check circulation and safety controls. |
| Low pressure |
System pressure too low |
Top up pressure to 1.0 to 1.5 bar. If it drops again within days, call an engineer. |
| Fan / airflow |
Airflow proving or fan issue |
Call an engineer. Do not attempt DIY on flues. |
| Sensor fault |
Temperature or system sensor issue |
Reset once. If it returns, call an engineer for testing. |
| Circulation / flow |
Restricted flow or pump related issue |
Check radiators are warming evenly. If it returns, call an engineer. |
Most Searched Viessmann Problems
If you are seeing a lockout, loss of hot water, or your Viessmann boiler keeps resetting, tell us the fault code and model and we will confirm the safest next step.
F4 – ignition failure
F4 is the most common Viessmann fault code. The boiler is attempting to ignite but no flame is detected. Common causes include gas supply issues, a faulty ignition electrode, or a blocked condensate pipe in winter. Check gas is on elsewhere in the home. Try one reset. If the lockout returns, stop and call an engineer.
Low pressure
If your Viessmann shows a low pressure warning, system pressure has dropped below the minimum threshold. Top up via the filling loop to around 1.0 to 1.5 bar when cold. If pressure drops again within days, there may be a leak in the system or a failing expansion vessel. Call an engineer to find the cause.
F2 – overheat protection
If your Viessmann shows F2, the boiler has overheated and locked out for safety. This can indicate a circulation problem, pump failure, or blocked heat exchanger. Do not keep resetting. Call an engineer to check the system.
No hot water but heating works
On Viessmann combi boilers, you may get heating but no hot water, or the reverse. This often points to a diverter valve issue. The diverter valve directs hot water between taps and radiators. When it wears or sticks, hot water delivery becomes unreliable. Call an engineer for diagnosis.
Why Viessmann Boilers Develop Faults
Viessmann is a German manufacturer known for high-quality engineering. Here is what we commonly see.
Ignition electrode wear
Ignition faults (F4) can occur when the ignition electrode wears or becomes coated with carbon. Condensate blockages in winter can also contribute to repeated lockouts.
Low pressure and expansion vessel faults
Low pressure faults often point to a failing expansion vessel or a weeping pressure relief valve. The expansion vessel absorbs pressure changes as water heats and cools. If the diaphragm fails or the air charge is lost, pressure drops can occur.
Circulation and flow issues
Restricted flow can indicate poor circulation through the system. This may be caused by a failing pump, sludge buildup, or closed radiator valves. A powerflush may help restore flow.
Fan and airflow faults
Fan faults prevent safe combustion and flue gas extraction. The boiler will lock out for safety. Causes include fan motor failure, wiring faults, or flue blockages.
Diverter valve on combi boilers
The diverter valve directs hot water between your taps and radiators. When it wears or sticks, you may get heating but no hot water, or the reverse.
Viessmann Models We Repair
We repair Viessmann combi, system, and regular boilers in London, including:
Vitodens 050-W: Entry-level combi and system boilers
Vitodens 100-W: 100-W B1GA, 100-W B1HA, 100-W B1KA
Vitodens 111-W: Storage combi with integrated cylinder
Vitodens 200-W: Premium range with higher efficiency
Vitodens 222-F: Floor-standing combi with cylinder
Vitodens 300-W: Top-of-range condensing boiler
Viessmann parts are available through their UK network. We check availability before attending and advise honestly if repair is not viable or cost effective.
Repair or Replace Your Viessmann Boiler?
We help you decide based on age, reliability, and parts availability.
Repair makes sense when
- Boiler is under 10 years old
- This is the first major fault
- Parts are readily available
- Boiler has been regularly serviced
Replacement may be better when
- Boiler is 12 to 15 years old or more
- You have had multiple breakdowns recently
- Parts are obsolete or hard to source
- The boiler is undersized for the property
- Energy bills are higher than expected for the property size
Our engineers give honest assessments. We focus on safety and reliability, not pushing unnecessary replacements.
Viessmann Boiler Servicing
Annual servicing reduces breakdown risk and keeps your Viessmann boiler running efficiently. See Boiler servicing London.
Landlords and Letting Agents
We provide boiler repairs and gas safety certification for landlords across London. See Landlord gas safety certificate (CP12).
Viessmann Repairs Across London
London wide coverage for Viessmann boiler repairs. Book an engineer or view our London areas we cover.
Have your postcode and fault code ready and we will confirm the quickest appointment slot.
Other Boiler Brands We Repair
Worcester • Vaillant • Ideal • Baxi • Glow-worm • Main • Potterton • Vokera • Alpha • Ferroli
View all brands
Viessmann Boiler Repair FAQs
How quickly can you attend for a Viessmann breakdown?
We offer same day attendance where slots are available. For no heating or hot water, we prioritise urgent breakdowns. Call our 24/7 line and we will advise availability.
Do you carry Viessmann parts?
We stock common Viessmann parts including diverter valves, ignition electrodes, pressure sensors, and PCBs. For less common parts, we can usually source within 24 to 48 hours.
Is it safe to reset my Viessmann boiler?
Try one reset. If the fault returns after resetting, stop and call an engineer. Do not keep resetting, especially for F2 faults.
How much does a Viessmann boiler repair cost?
Costs vary depending on the fault and parts required. We diagnose first and quote before any repair work begins.
Related Services
Speak to Our Team
For safe next steps, call now.
Call 0203 868 6251 | Book an Engineer
Gas Safe registered • 24/7 call handling • Quote before work
