Why Combustion Testing Matters When Installing a Regular OR Tankless Combination Boiler

A natural-gas tankless combination boiler is a sophisticated appliance designed to provide both space heating and domestic hot water efficiently. However, even a high-quality boiler cannot be expected to perform properly simply because it has been mounted on the wall and connected. Correct commissioning is essential.

Homeowners should hire a licensed, qualified plumber or heating contractor who has been trained to use a calibrated combustion analyzer and understands the manufacturer’s commissioning procedures. This instrument measures important combustion values, such as oxygen, carbon monoxide, carbon dioxide, flue-gas temperature, and calculated combustion efficiency. The technician can then compare the readings with the ranges specified by the original equipment manufacturer.

This testing is important for several reasons:

• Safety: Improper combustion can produce elevated carbon monoxide levels. Testing helps confirm that the boiler is burning gas safely and that its venting system is operating correctly.
• Efficiency: Incorrect combustion settings can waste fuel and increase heating costs. Proper commissioning helps the boiler perform as closely as possible to the manufacturer’s specifications.
• Reliability: A poorly adjusted appliance may experience ignition problems, nuisance shutdowns, overheating, or premature component failure.
• Warranty documentation: A dated combustion report can help demonstrate that the boiler was properly commissioned and maintained.
• Accountability: A printed report gives the homeowner measurable evidence of the system’s operating condition instead of relying only on a verbal assurance that “everything looks fine.”

Installation conditions—including gas pressure, fuel composition, venting, altitude, and air supply—can affect combustion. In some cases, a gas valve may require a minor adjustment after installation. Such adjustments must be performed only by a qualified technician, using a calibrated analyzer and following the manufacturer’s exact procedures. A gas valve should never be adjusted by eye, by flame appearance alone, or without proper testing.

At the completion of a new installation, the contractor should test the boiler at the firing rates required by the manufacturer and provide the homeowner with a printed combustion report. The report should identify the appliance, date, technician, operating mode or firing rate, and measured combustion values. Ideally, these readings should also be recorded on the manufacturer’s commissioning form and retained with the boiler’s service records.

Combustion testing should also be included in annual maintenance. During each service visit, the technician should inspect and clean the boiler as required, verify gas supply and venting, test safety controls, and perform combustion analysis in accordance with the manufacturer’s instructions. A fresh printed report should be given to the homeowner after every annual service. Comparing reports from year to year can reveal changes before they become expensive or dangerous problems.

Homeowners should ask prospective contractors a few direct questions:

1. Are you trained and licensed to install and service this specific boiler?
2. Will you commission it according to the manufacturer’s instructions?
3. Do you use a calibrated combustion analyzer?
4. Will you test all manufacturer-required firing rates?
5. Will you provide a printed combustion report when the work is complete?

A combustion printout is not merely an optional piece of paper. It is valuable documentation that the contractor performed essential testing and that the boiler’s measured combustion values were checked against the manufacturer’s requirements. Choosing a technician with the proper knowledge and equipment helps protect the homeowner’s safety, comfort, investment, and long-term energy costs.