FAQ
TL;DR: After a swap to a Vaillant atmoMAG, ignition delay grew from ~1.5 s to several seconds; “It’s just blowing.” [Elektroda, marek.nosal, post #16828625]
Why it matters: Slow ignition or blowback on a gas water heater can signal airflow, electrode, or pressure setup faults that risk damage and safety; this FAQ helps DIYers and homeowners ask the right questions and tests before calling service.
Quick Facts
- Reported install fee: PLN 150 for swap-in, hoses, gas pipe, and wall clamp. [Elektroda, marek.nosal, post #16828625]
- Replaced Saunier Duval Opalia C11E with Vaillant atmoMAG mini 11-0 XI H. [Elektroda, marek.nosal, post #16828676]
- Symptom set: ignition after “a few seconds,” blowback, prior unit lit in ~1.5 s. [Elektroda, marek.nosal, post #16828625]
- First checks: room air supply, no mechanical exhaust fan, electrode gap, and gas pressure settings. [Elektroda, dobroslaw, post #16829239]
What does “it blows” on a gas water heater actually mean?
In this thread, “it blows” describes flame blowback or escape, including reports of flame going behind the casing. That points to delayed ignition or disturbed combustion. Do not ignore visible flame outside intended ports. Pause use and have a qualified technician inspect combustion and sealing immediately to avoid damage. Document the behavior with video for service records. “Flame escapes behind the furnace casing” is a key symptom to report during service calls. [Elektroda, marek.nosal, post #16839073]
Why is my Vaillant atmoMAG lighting slowly compared to my old Opalia?
Slow ignition can follow poor air supply, a prohibited mechanical exhaust fan, an oversized ionization/ignition electrode gap, or unadjusted gas pressure. A small backflow at start can also delay lighting. Open a window to test airflow influence. Technicians should verify electrode spacing and set pressures to the appliance spec. “Check air supply and chimney path” is the first recommendation. [Elektroda, dobroslaw, post #16829239]
How can I safely quick-test whether delayed ignition is an ignition issue?
Use this simple check suggested by a contributor. 1) Hold a lit match or lighter at the ignition electrode area. 2) Open the hot-water tap to start the heater. 3) Watch whether the burner lights promptly and burns evenly. If it lights faster with a helper flame, the ignition path or timing needs adjustment. Verify burn uniformity across all burner sections and note knob positions for power and temperature. [Elektroda, krzsboj, post #16850564]
Can a bathroom fan cause blowback or slow starts?
Yes. For open-flue water heaters, a mechanical exhaust in the bathroom is not permitted because it can pull combustion gases and disrupt draft. The device needs room air supply and a gravity exhaust path. A start-up backflow creates ignition delay and rough lighting. Test with the window open and any fans off. If performance improves, fix ventilation compliance before adjusting the heater. [Elektroda, dobroslaw, post #16829239]
What should a proper post-installation check include?
Confirm correct installation per trade practice, an unobstructed chimney, and verified maximum and minimum gas pressures. Ensure permanent air supply to the room plus a gravity exhaust. If these pass, the heater should operate cleanly without blowback. When an authorized tech says it is “good,” but symptoms persist, seek a second authorized opinion to identify setup gaps. [Elektroda, dobroslaw, post #16840044]
How do I document issues if the authorized service says “it’s fine”?
Record videos showing ignition delay and any flame escaping the casing. Note window position, fan status, and knob settings. Keep timestamps and model details. Then request another authorized technician; an additional service opinion can propose a solution even if the first visit found no fault. Independent experts add cost without warranty leverage, so try a second authorized visit first. [Elektroda, dobroslaw, post #16840044]
What ignition time is typical for a working unit like this?
In the case described, the prior Opalia lit in about 1.5 seconds, while the replacement often takes several seconds. That change signals a setup or condition difference worth investigating. Use the old performance as a practical benchmark for your piping and draft conditions. Significant deviation under similar conditions justifies adjustment and venting checks. [Elektroda, marek.nosal, post #16828625]
Could the ignition or ionization electrode gap be wrong?
Yes. A too-large gap can delay spark transfer and flame detection. One tech bent electrodes during a visit, but the issue remained, indicating the need for precise adjustment and verification. Have an experienced technician set the gap per the appliance spec and confirm stable ignition at low and high flow. “Too large gap” was specifically flagged. [Elektroda, dobroslaw, post #16829239]
Could incorrect gas pressure settings be the culprit?
Yes. Incorrect minimum or maximum gas pressures can cause delayed ignition, lift-off, or uneven burner lighting. An authorized technician should measure and adjust both settings during commissioning. Without confirmed pressures, other tweaks mask the root cause. After pressures are set and airflow assured, reassess ignition. This is a standard commissioning step. [Elektroda, dobroslaw, post #16840044]
What ventilation should a bathroom with an open-flue heater have?
Provide a permanent air supply from outside and a gravity (non-mechanical) exhaust path. Do not use a powered exhaust fan with an open-flue water heater in the room. Start-up backflow hints at inadequate draft or supply. Test with the window open; if behavior improves, correct ventilation before adjusting the heater. [Elektroda, dobroslaw, post #16829239]
What if flame escapes behind the casing during startup?
Stop using the appliance until inspected. Flame outside intended areas indicates delayed ignition or leakage paths that can scorch components and risk corrosion. Report this exact symptom to the technician and include video evidence. If dismissed, request a second authorized service visit and reference your recordings. This edge case was noted by the owner. [Elektroda, marek.nosal, post #16839073]
Should I remove the housing to diagnose, and what else to check?
A contributor advised checking operation without the housing to observe ignition. If no improvement, examine the servo mechanism closely. Also confirm water supply and discharge are not restricted and that filters are clean. These steps help separate airflow effects from control or flow faults. Reassemble safely after inspection. [Elektroda, kz61, post #16830335]
Was PLN 150 a reasonable installation price?
The thread notes PLN 150 for swapping the same type unit. Another user said a good installer would not accept such a job for that price, especially during the heating season. Underpricing can correlate with rushed commissioning and missed adjustments. Budget for proper setup and verification. [Elektroda, dobroslaw, post #16829239]
What details should I include when asking for help online?
Always state the exact device model and version in your first post. Missing model info delays diagnosis. Include symptoms, videos, venting type, any fans, and the distance to windows or grilles. Add prior unit behavior for comparison. “Write what device it is” was the first moderation nudge here. [Elektroda, kz61, post #16828660]
I forgot.
