FAQ
TL;DR: If your Immergas combi (e.g., NIKE STAR 24 3 E) needs cleaning every 6 months, suspect airflow, deposits, or duct corrosion; “aluminum spiro tube … strongly corrodes.” [Elektroda, Michał643, post #18729713]
Why it matters: Frequent fouling leads to CO alarms, poor DHW performance, and risky ignition events. This FAQ is for tenants, owners, and techs troubleshooting green‑white residue, ash, and recurring cleanings.
Quick Facts
- Model reported: Immergas NIKE STAR 24 3 E, open chamber, natural gas; DHW 45°C, CH 55°C setpoints. [Elektroda, Ursus81, post #16814466]
- Symptom chain: ash under boiler → CO alarm during high DHW load → flue smell → DHW heating failure. [Elektroda, Ursus81, post #16804352]
- Suspected causes: mismatched gas nozzles or incorrect gas pressure; require pro service. [Elektroda, 762302, post #16804405]
- Remediation tips: straighten heat‑exchanger fins; ensure clean burner/mixing chamber; set min/max gas correctly. [Elektroda, mirrzo, post #16836216]
- Edge case: green‑white flakes from corroding aluminum spiro duct; vacuum fouling about every 6 months. [Elektroda, Michał643, post #18729713]
Why is there a green‑white precipitate on my Immergas heat exchanger?
Users traced green‑white flakes to corrosion of an aluminum spiro exhaust duct. The corrosion products drop onto the exchanger and burners, forming deposits that char into ash. Replace any non‑rated aluminum spiro with a proper flue component. As one poster notes, “aluminum spiro tube … strongly corrodes,” leading to recurring fouling and ignition issues. Cleaning helps temporarily, but source elimination fixes recurrence. [Elektroda, Michał643, post #18729713]
Is cleaning every six months normal for this boiler?
No. Semiannual tear‑downs suggest an upstream issue, not normal wear. In the thread, owners report needing to vacuum nozzles and the exchanger about every six months only when a corroding aluminum spiro duct sheds debris. Address the root cause (ducting, air, gas setup) to extend intervals. Routine annual service is typical, but twice‑yearly deep cleans indicate a fault or misapplication. [Elektroda, Michał643, post #18729713]
Could wrong gas nozzles or pressure cause soot and ash?
Yes. A technician flagged symptoms consistent with mismatched nozzles for the gas type or incorrect gas pressure. Both conditions skew combustion, increasing soot and residue. Do not DIY gas adjustments. Schedule a qualified service visit to verify injector size and set pressures at minimum and maximum output. “Better not risk it,” as the poster advises. [Elektroda, 762302, post #16804405]
Why does the CO alarm trigger after evening baths or high DHW demand?
During long, hot showers the boiler fires harder. Any blocked fins, falling duct corrosion, or dirty burner increases incomplete combustion. Owners noticed the alarm only under high DHW load, progressing to flue smell and DHW failure as fouling worsened. Restoring clear exchanger passages and clean ignition/combustion zones resolves the sequence. Document events to share with your technician. [Elektroda, Ursus81, post #16804352]
How do I safely clean the exchanger and burner when ash builds up?
- Power off and cool. Remove casing. Vacuum loose ash around nozzles and exchanger.
- Gently straighten bent fins to restore exhaust flow. Do not puncture or deform tubes.
- Clean burner/mixing chamber, then have a pro adjust min/max gas settings.
This restores airflow and flame quality, but address upstream causes to prevent repeat fouling. [Elektroda, mirrzo, post #16836216]
What does a correct flame look like on this open‑chamber model?
A healthy flame appears low and blue. A yellow, tall, or lazy flame suggests poor air, fouled burner, or gas setup issues. A contributor asked whether the flame was yellow and high or low and blue to guide diagnosis. If viewing is difficult, prioritize cleaning, airflow checks, and professional adjustment. [Elektroda, dobroslaw, post #16814664]
Could ventilation or chimney draft be the problem?
Yes. The room needs reliable air intake and clear gravity ventilation, and the flue must draft correctly. One helper requested details on gas type, chamber type, installation model, and whether mechanical extraction or grills were present to assess air supply. Verify intake openings and have draft measured by a pro. [Elektroda, dobroslaw, post #16806216]
My installer says air intake can be partly closed—should I?
Be cautious. An owner reported advice to reduce intake because the room was cooling, yet fouling recurred every six months regardless of intake position. Limiting air can worsen combustion quality. Keep dedicated combustion air available and fix root causes like duct corrosion or gas setup. [Elektroda, Ursus81, post #16816329]
What’s a spiro tube, and does it belong on a gas boiler flue?
A spiro tube is a spiral‑wound flexible duct, often aluminum. A user found an aluminum spiro used on the boiler flue corroded rapidly, shedding green‑white debris onto the exchanger and nozzles. Replace such ducting with flue components rated for gas appliances to stop contamination and ignition issues. [Elektroda, Michał643, post #18729713]
What system details were reported in this case?
The setup: Immergas NIKE STAR 24 3 E, open chamber, natural gas, DHW 45°C, CH 55°C. The home had a utility room installation with intake below the boiler and ceiling ventilation nearby. These specifics help techs match parts and settings during diagnosis. Share them when booking service. [Elektroda, Ursus81, post #16814466]
How large an area did the boiler heat, and what emitters?
One owner heated about 100 m² with panel radiators. This context suggests the unit size is broadly appropriate, so recurrent fouling likely stems from combustion air, flue materials, or gas setup rather than chronic oversizing alone. Provide area and emitter types when consulting service. [Elektroda, Ursus81, post #16825195]
When should I call a licensed service technician?
Immediately if you see ash buildup, smell flue gases, or your CO alarm triggers. A contributor emphasized that nozzle selection and gas pressure setting are not DIY tasks. Book professional calibration at minimum and maximum power after cleaning and airflow restoration. Safety first. [Elektroda, 762302, post #16804405]
Why straighten bent heat‑exchanger fins?
Bent fins restrict flue gas paths, raising backpressure and promoting incomplete combustion and soot. A technician recommended straightening fins, cleaning the burner/mixing chamber, and adjusting gas at min/max. This reduces deposits and CO alarms under high DHW load. Use a fin comb and gentle pressure. [Elektroda, mirrzo, post #16836216]
I’m a tenant. How can I document issues to convince the owner/installer?
Log dates of CO alarms, flue smells, DHW failures, and cleaning intervals. Photograph ash around the pump and exchanger fins after removing the housing. One tenant gathered evidence to discuss with the owner and installer when reassurances conflicted with recurring faults. Clear records speed resolution. [Elektroda, Ursus81, post #16836254]
What failure risks occur if I ignore the debris?
Fouling progressed to flue odors, CO alarm activation, and finally DHW heating failure in the reported case. Another user reported explosive ignitions when debris covered nozzles and the spark gap. Address deposits and replace corrosive ducting promptly to avoid hazardous starts. [Elektroda, Michał643, post #18729713]
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