Heating Tech

Why Won’t the Furnace Run?

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It’s a bad sign if a furnace is starting and stopping too often (short cycling). It’s bad if it’s just running all the time. What could be a worse sign? Well, what’s it mean if the furnace won’t start in the first place? At least if your furnace short-cycles, you’ve got heat and you know it’s not a catastrophic failure. Things get scary when it won’t cycle at all.   The Easy Suspects Your furnace isn’t running. Don’t panic yet. If we were to round up every contractor in our books and ask about simple break downs, the stories would never end. Simple, cheap, and even silly things can bring on the chill. We think the most common ones are: Ran Out of Fuel Empty tank Clogged fuel line Gas main shut off Electrical Shut Off Someone bumped a shut off switch Breaker tripped during storm Failed switch or contactor stuck in the off position Thermostat Wire Cut Wires chewed by a mouse Wires damaged with nails or screws in the wall Chimney blocked With debris With a birds’ nest Minor Hardware Failure Bad Pilot light Bad ignitor Bad flame sensor   When we say these are common events, we really mean it. I’ve experienced at least three of these. My home furnace is a nice little oil burner, and we’ve run it dry during the winter. We’ve discovered our fuel pipe doesn’t dip to the bottom of the tank. […]

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Heating Tech

What is a Flame Sensor?

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If a roll out switch is a master “things have gone horribly wrong, stop the show” switch and thermisters are basically limited to measuring temperature, how do we know the burner is actually making a flame? Sure, the thermister will read heat, but that takes time. Imagine the igniter has failed, it takes maybe 10-40 seconds to register enough heat to confirm a flame. The combustion chamber is now pumped full of a potentially explosive fuel mixture and nothing is happening. We need something much, much faster, we need a flame sensor.   How Not to Detect a Flame The way a person knows something is on fire is usually the bright flames and the fact that sticking their hand near it becomes really painful. This approach doesn’t quite work for a furnace. We could measure the light output, that requires more processing power to interpret the data, some incredibly sensitive hardware to detect the tiniest start of a flame, and it doesn’t work on every fuel type. There are systems that work this way, but it’s a little more expensive. We could measure the temperature, but we run into challenges with making a sensor you can shove in the heart of a flame for years on end without failure. It has been done, but it’s expensive. There are however, laws of physics we can exploit to detect a flame without anywhere near so many challenges. We can detect a […]

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