Precautions must be taken to prevent degradation of building materials by flue products
The A16 error code on Modine boilers indicates precautions must be taken to prevent degradation of building materials by flue products.
Modine A16 means: precautions must be taken to prevent degradation of building materials by flue products. The usual causes are precautions must be taken to prevent degradation of building materials by flue products, single wall vent pipe must not pass through any unoccupied attic, inside wall, concealed space, or floor or uninsula. You can safely reset the boiler once — if A16 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does A16 Mean
The A16 code is shown by the boiler’s control board when it detects precautions must be taken to prevent degradation of building materials by flue products. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows A16 and the boiler stops until the fault is cleared |
Common Causes
Causes documented in 1 technical sources.
| Cause |
|---|
| Precautions must be taken to prevent degradation of building materials by flue products. |
| Single wall vent pipe must not pass through any unoccupied attic, inside wall, concealed space, or floor. |
| Uninsula |
Safety Warning
A16 involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
Visually inspect the flue terminal outside — check for blockages, birds' nests, or ice
Check the flue run — verify it is within the manufacturer's maximum length and number of bends
Perform a flue gas analysis — CO and CO2 levels should be within specification
Check the condensate drain — ensure it is not blocked
Verify the air intake is not obstructed (for room-sealed appliances)
Check for signs of flue gas spillage in the room (for open-flue appliances)
How to Fix It
Clear any flue blockage
correct the flue installation if it exceeds maximum length or bends
clear ice from the flue terminal (insulate external condensate pipe)
clear the condensate drain
if combustion analysis shows incorrect values, adjust the gas valve or service the burner
Refer to the Modine service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
Diagnostic Tools
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Affected Models
Modine models that can display fault code A16:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Modine models | — | Possible |
Frequently Asked Questions
Clear any flue blockage. According to the technical documentation, this is the first check on the list for A16.
A16 is not classified as a high-severity fault, so the boiler can be reset once. If A16 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.