Viessmann Vitodens 100-W fault 348
Gas modulation valve
Gas boilerWhat it means
Burner in a fault state related to the gas modulation valve, which may be caused by multiple heat generators sharing a flue system without correct configuration, or flue restrictions.
Likely causes
- Gas modulation valve fault
- Multiple heat generators on common flue system not configured correctly
- Restricted flue system flow
- Simultaneous operation of boiler and air-extracting appliances
- Negative pressure created by extractor hoods, extractors, air conditioning units, or central vacuum cleaning systems
Where to start
- If several heat generators are connected to a common flue system: Check whether "Multiple connections" is set in the commissioning assistant.
- Check the flue system for unrestricted flow.
- Turn off the ON/OFF switch.
The full answer, free
- 17 more checks in order
- The readings and component tests from the manual
- How to put it right, step by step
- The manual page for this fault (page 74), right under the answer
Safety: Isolate gas and power before you open the case. If you have been into the gas side, do a tightness test, and a combustion and flue check before you hand back. Gas Safe (UK) or RGI (Ireland) work only.
From the Viessmann manual for the Vitodens 100-W. Check the model on the data plate before you order parts.
Other Viessmann Vitodens 100-W fault codes
- 100PlusBus voltage error
- 12Short circuit, collector temperature sensor
- 161HBMU heat management unit data memory access fault
- 162Processor low voltage
- 163Checksum error, data memory access, HBMU heat management unit
- 176Condensate backup in the heat cell
- 346Ionisation current calibration error
- 347Flue gas recirculation
- 349Air mass rate flow not detected correctly in fan unit
- 350Ionisation current lies outside the permissible range
- 351Ionisation current lies outside the permissible range
- 352Combustion CO limit exceeded
- 355Analogue signal reference check: flame signal already present at burner start
- 359No ignition spark, burner in fault state
- 361Flame signal not present or insufficient at burner start
- 364Internal fault, burner in fault state
- 368Gas pressure switch fault, burner locked out
- 369Flame lost immediately after flame formation (during safety time)
- 371Fan speed too low
- 372Repeated flame loss during calibration
- 373Heat transfer too low during calibration, temperature limiter shut down
- 374Burner restarts, stabilisation conditions for pre-calibration not met
- 375Ionisation current calibration not performed
- 376Ionisation current differential not plausible