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Viessmann · Boiler troubleshooting

Condensate not draining, burner shuts down

What is going on

If condensate cannot leave the boiler it collects in the lower part and the burner stops with a fault message (F.540 / A.18).

Likely causes

  • Blocked siphon or drain hose
  • Hose without constant fall
  • Neutralizer blocked

Check in this order

  1. Cover electronics, move the control unit to service position, pull off the supply hose and remove the siphon.
  2. Clean the siphon, refill with water and refit with the clip secure.
  3. Route the drain hose with constant fall and no bends; keep an air gap before any neutralizer.
  4. Do not connect other appliance drains (e.g. softener backwash) to the boiler condensate line.
  5. On common venting, also clean the siphon in the flue gas collector.

Applies to: Vitodens 200-W B2HE 85, 120, 150, 199

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Source: Viessmann Vitodens 200-W B2HE 85/120/150/199 Service Instructions 6167 813-24 (09/2026), p.31-32. Written in our own words; check the manual for your exact model.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.