This error indicates the burner sensor has exceeded 199ºF. The burner will re-fire once the burner temperature drops below 181ºF. If this occurs more than five times in ten minutes during a single heat demand, an F28 lockout code is generated.
- Check sensor by turning off the gas and allowing the unit to go through pre-purge and post purge cycles. While air is flowing through the burner check the burner sensor value on the display. This value should similar to the current intake air temperature. If this value is much different than the current intake air, check sensor resistance and wiring. If resistance values are out of range replace sensor.
- If sensor is ok, check combustion, often a rich combustion setting elevates burner temperatures. Ensure there are no blockages on either the intake or the exhaust. Confirm the combustion is set to proper CO2 numbers, especially on low fire. After adjusting combustion, restart the boiler and observe the burner temperature on the display. This should be done both on high and low fire.
