Applicable Systems
Vitodens
Symptoms
The boiler fails to ignite after three consecutive attempts. The flame detection circuit does not confirm a flame and the controller enters a lockout state.
Possible Causes
- Ignition electrode gap too wide or fouled with carbon buildup
- Gas valve not opening or gas pressure below the minimum required for ignition
- Flame sensor rod contaminated or cracked, failing to detect the flame
- Ignition transformer failed, not producing the high-voltage spark
Troubleshooting Steps
- Step 1: Inspect and clean the ignition electrode and flame sensor rod
Electrode gap should be 3-5mm; clean with emery cloth - Step 2: Check the gas inlet pressure at the test port with a manometer
Natural gas should read 7-11 inches water column at the inlet - Step 3: Test the ignition transformer by measuring spark output with a spark tester
A strong blue spark should jump the gap; replace if weak or absent - Step 4: Verify the gas valve opens by listening for the click during the ignition sequence
If silent, test the valve coil resistance and control voltage
How to Reset
Reset: Press and hold the reset button on the boiler controller for 3 seconds. If lockout recurs, do not attempt further resets - call a qualified technician.
Common Replacement Parts
- Ignition electrode: OEM-specified, includes ceramic (Match to boiler model)
- Flame sensor rod: Single-rod or dual-rod type (Clean with emery cloth, not sandpaper)
- Ignition transformer: 120V primary, 10kV secondary (Match to boiler model)
Frequently Asked Questions
- Q: How many times can I press reset?
Maximum 3 times within 10 minutes. Repeated lockouts indicate a serious fault requiring professional service.
- Q: What gas pressure do I need?
Natural gas: 7-11 inches WC inlet. Propane: 11-13 inches WC. Verify with a manometer before adjustment.
- Q: How often should I service the ignition?
Annually before heating season. Clean electrodes, check gas pressure, and verify flame signal strength (minimum 2 microamps DC).
Source: OEM Installation Manual
Category: Home Boiler