Viessmann
The Viessmann Vitodens 100 W type WB1B 7.9 to 35Kw is a wall-hung condensing system boiler with a heating output range of 7.9 kW to 35 kW, suitable for natural gas and LPG.
The Viessmann Vitodens 100 W type WB1B 7.9 to 35Kw is a wall-hung system boiler, introduced in 2012, designed for domestic heating applications in the UK. This appliance operates as a condensing unit, compatible with both natural gas and LPG fuel types. It provides a heating output range from 7.9 kW to 35 kW, making it suitable for various property sizes. This page details its technical specifications, common fault codes, and installation requirements for heating engineers and homeowners.
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Full technical specifications extracted from the manufacturer brochure. Empty sections are hidden.
Heating flow Ø 22 mm, Heating return Ø 22 mm, Condensate drain Ø 22 mm, Gas connection R 1½
Soften fill water harder than 300 ppm.
The Viessmann Vitodens 100-W Type WB1B is a system boiler engineered for efficient central heating. It delivers a heating output between 7.9 kW and 35 kW, making it adaptable for diverse property demands. The appliance is designed for wall-hung installation, featuring compact dimensions of 600 mm height, 375 mm width, and 151 mm depth, with a dry weight of 32 kg.
Electrical requirements include a 230 V, 50 Hz supply, protected by a 3 A fuse, with a maximum power consumption of 65 W. This model incorporates OpenTherm compatibility and supports weather compensation, allowing for optimised system control. Safety features include overheat and low water protection, alongside frost protection. The minimum operating pressure for sealed unvented systems is 0.8 bar. Gas connections are rated for 20 mbar for natural gas and 37 mbar for LPG. Condensate drainage requires a 22 mm pipe. Installation guidelines specify a minimum bottom clearance of 5 mm and advise softening fill water exceeding 300 ppm hardness.
Every fault code listed in the manufacturer brochure, with likely causes and engineer actions. Each code has a permalink — paste a URL like https://www.boilertag.com/boilers/viessmann/viessmann-vitodens-100-w-type-wb1b-7-9-to-35kw#fault-f9 to jump straight to the entry.
| Code | Meaning | Details |
|---|---|---|
| F9Lockout | Burner in a fault state Show causes & actionsFan speed too low during burner start Likely causes
Engineer action Check fan, fan connecting cables and power supply; check fan control. Reset procedure Press "Reset" (see page 36). | Details |
| F4Lockout | Burner in a fault state Show causes & actionsNo flame signal detected Likely causes
Engineer action Check the ionisation electrode and connecting cables, check the gas pressure, check the gas train, ignition, ignition module and condensate drain. Reset procedure Press "Reset" (see page 36). | Details |
| 10 | Constant mode Show causes & actionsShort circuit, outside temperature sensor Likely causes
Engineer action Check the outside temperature sensor and lead (see page 38). | Details |
| 18 | Constant mode Show causes & actionsLead break, outside temperature sensor Likely causes
Engineer action Check the outside temperature sensor and lead (see page 38). | Details |
| 30Lockout | Burner blocked Show causes & actionsShort circuit, boiler water temperature sensor Likely causes
Engineer action Check the boiler water temperature sensor (see page 39). | Details |
| 38Lockout | Burner blocked Show causes & actionsLead break, boiler water temperature sensor Likely causes
Engineer action Check the boiler water temperature sensor (see page 39). | Details |
| 50 | No DHW heating Show causes & actionsTerminal box cylinder demand fault Likely causes
Engineer action Check terminal box connections and replace the terminal box if required. | Details |
| 58 | No DHW heating Show causes & actionsTerminal box cylinder demand fault Likely causes
Engineer action Check terminal box connections and replace the terminal box if required. | Details |
| 60Lockout | Burner blocked Show causes & actionsShort circuit, return temperature sensor Likely causes
Engineer action Check the return temperature sensor (see page 39). | Details |
| 68Lockout | Burner blocked Show causes & actionsLead break, return temperature sensor Likely causes
Engineer action Check the return temperature sensor (see page 39). | Details |
| A9 | Control mode without Open Therm device Show causes & actionsCommunication error Open Therm device Likely causes
Engineer action Check connections and cable; replace Open Therm device if required. | Details |
| b0Lockout | Burner blocked Show causes & actionsShort circuit, flue gas temperature sensor Likely causes
Engineer action Check the sensor (see page 41). | Details |
| b8Lockout | Burner blocked Show causes & actionsLead break, flue gas temperature sensor Likely causes
Engineer action Check the sensor (see page 41). | Details |
| E5Lockout | Burner blocked Show causes & actionsInternal fault Likely causes
Engineer action Check the ionisation electrode and connecting cables. Reset procedure Press "Reset" (see page 36). | Details |
| F0Lockout | Burner blocked Show causes & actionsInternal fault Likely causes
Engineer action Replace control unit. | Details |
| F1Lockout | Burner in a fault state Show causes & actionsMax. flue gas temperature exceeded Likely causes
Engineer action Check heating system fill level. Check circulation pump. Vent the system. Reset procedure Press "Reset" (see page 36). | Details |
| F2Lockout | Burner in a fault state Show causes & actionsThe temperature limiter has responded Likely causes
Engineer action Check heating system fill level. Check circulation pump. Vent the system. Check temperature limiter and connecting cables. Reset procedure Press "Reset" (see page 36). | Details |
| F3Lockout | Burner in a fault state Show causes & actionsFlame signal is already present at burner start Likely causes
Engineer action Check ionisation electrode and connecting cable. Reset procedure Press "Reset" (see page 36). | Details |
| F8Lockout | Burner in a fault state Show causes & actionsFuel valve closes too late Likely causes
Engineer action Check gas train. Check both control paths. Reset procedure Press "Reset" (see page 36). | Details |
| FALockout | Burner in a fault state Show causes & actionsFan not at stand-still Likely causes
Engineer action Check fan, fan connecting cables and fan control. Reset procedure Press "Reset" (see page 36). | Details |
| FCLockout | Burner blocked Show causes & actionsElectrical fan control (control unit) faulty Likely causes
Engineer action Check fan connecting cable; if required, replace or replace control unit. Reset procedure Press "Reset" (see page 36). Replace control unit if fault persists. | Details |
| FdLockout | Burner blocked Show causes & actionsFault, burner control unit Likely causes
Engineer action Check ignition electrodes and connecting cables. Check whether a strong interference (EMC) field exists near the appliance. Reset procedure Press "Reset" (see page 36). Replace control unit if fault persists. | Details |
| FFLockout | Burner blocked Show causes & actionsFault, burner control unit Likely causes
Engineer action Check ignition electrodes and connecting cables. Check whether a strong interference (EMC) field exists near the appliance. Reset procedure Press "Reset" (see page 36). Replace control unit if fault persists. | Details |
Patterns that group across the manufacturer's fault-code table. Each entry links to the full code listing further down the page.
Engineer: Check fan, fan connecting cables and power supply; check fan control.
Triggered by fault code F9.
Engineer: Check the boiler water temperature sensor (see page 39).
Triggered by fault code 30.
Engineer: Check the outside temperature sensor and lead (see page 38).
Triggered by fault code 10.
Engineer: Check terminal box connections and replace the terminal box if required.
Triggered by fault code 50.
Engineer: Check connections and cable; replace Open Therm device if required.
Triggered by fault code A9.
Common questions from engineers and homeowners about the Viessmann Vitodens 100-W.
Parts referenced in the manufacturer brochure for routine service and repair.
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Specifications on this page are extracted from the manufacturer brochure. Always cross-check against the latest datasheet before commissioning or quoting. Last updated 28 June 2026.