Should flame sensor glow red?

Last Update: October 15, 2022

This is a question our experts keep getting from time to time. Now, we have got a complete detailed explanation and answer for everyone, who is interested!

Asked by: Jaren McClure
Score: 4.5/5 (20 votes)

The flame makes contact from the igniter/flame sensor to that grounded "hood like" thing above the flame. The rod will glow red during operation.

How do I know if my flame sensor is bad?

Signs of a bad furnace flame sensor are:
  1. The furnace lights but then shuts down after a few seconds (short cycles)
  2. The porcelain on the flame sensor is cracked.
  3. The flame sensor is sooty or corroded.

What should flame sensor read?

When the flame lights, you should read between 0.5 and 10 microamps (μA), depending on the furnace. Readings between 2 and 6 are common.

Is the flame sensor supposed to be in the flame?

As the gas valve opens to begin the combustion process, the current is sent out from the sensor in order to detect the presence of heat from a flame. ... However, if the furnace flame sensor does not detect the presence of a flame within 10 seconds of the gas valve opening, it will shut the furnace down.

What does a corroded flame sensor look like?

The flame sensor can become corroded due to carbon buildup from the flame. ... If the burner light goes out within seconds of switching on the unit, this is a telltale sign of a dirty sensor. If you see soot clearly covering the sensor, then it's time for a cleaning.

Flame sensor, Flame rod, Flame Rectification

24 related questions found

How much does it cost to replace a flame sensor?

You can expect to pay between $350 and $500 for a new flame sensor if you call a furnace repair company.

How long does a flame sensor last?

Generally speaking, the flame sensor should be replaced every two to three years as preventative maintenance. Some technicians also recommend changing it any time that there is a flame current issue.

Can you test a flame sensor?

You can measure flame signal by putting your meter (capable of measuring micro amps) in line between the flame sensor and the wire that was connected to it (see picture). If you are reading anything under 5 uA (micro amps), it is likely that your flame sensor is dirty.

Can you bypass a flame sensor?

In short, you cannot bypass the flame sensor and manually light your furnace. Bypassing safety controls, even when possible, should never be done. ... Instead, you should try cleaning or replacing your flame sensor to get it and your furnace back to good working order.


What causes a flame sensor to go bad?

What Causes a Flame Sensor to Get Dirty? It's possible for a flame sensor to go bad; but more often than not, it is not broken, just dirty from carbon buildup. Because a flame sensor has a very low tolerance for variations in the reading it takes, the slightest coating of carbon can cause it to misread and shut down.

How do you test a flame sensor voltage?

Test to see if there is have voltage going to the flame sensor. Insert one probe into the female end of the terminal Page 7 Place a probe on flame sensor and then allow the furnace to cycle. In this example the meter is reading 1.7 micro amps. You need to have >1.0 micro amps for the furnace to continue its cycle.

What is the difference between a flame sensor and a thermocouple?

Thermocouples are used on standing pilot furnaces that have pilot lights. The thermocouple sits near the pilot light and gauges whether it's working properly, while the flame sensor detects that the burners are lit once they start to emit gas and the igniters light them up.

What voltage should a flame sensor be?

As the heating cycle begins, the furnace control board emits a low current voltage to the flame sensor. This is usually between 40-80 volts AC.


Can a furnace run without a flame sensor?

It is basically a safety device so that the furnace will only run if there is a flame. If the furnace goes on with no flame then there could be a gas buildup which could cause a dangerous situation. If the sensor doesn't detect the flame then it will automatically shut down the furnace.

Can I bend flame sensor?

The main problem with bending a flame sensor is that they can break off and then need to be replaced.

Can you bypass a flame rollout switch?

It is not safe or recommended that you bypass a flame rollout switch. Bypassing a flame rollout switch leaves your home vulnerable to some significant fire hazards. Certain problems, such as a damaged heat exchanger, are leading causes of furnace fires and are detected by rollout switches.

Can a furnace flame sensor work intermittently?

After a gas furnace opens the gas valve to allow gas into the combustion chamber, the furnace control board will monitor for proper ignition of the gas. ... A dirty flame sensor will generally cause occasional ignition failures, but will allow the furnace to fire and function properly the majority of the time.


Why does my heater flame keeps going out?

Your furnace has a limit switch that keeps it from running if the heat exchanger is too hot. Dirty filters, closed or blocked vents and other blockages in airflow are common causes of an overheated furnace. A bad limit switch. The limit switch may be bad and need to be replaced.