Gas Fireplace Repair: How Fireplaces Work
When it comes to gas fireplace repair, it is important to know which type you have and how they work, so that you can have a better understanding of why they might be malfunctioning when they start giving you problems.
There are basically 3 different types of gas fireplaces:
- Millivolt System Gas Fireplaces
- Standard System Gas Fireplaces (also called safety pilot systems)
- IPI System Gas Fireplaces
For diagnosing purposes it is easiest to categorize fireplaces by their control system. And probably the easiest way to tell which type of system your gas fireplace uses is to determine how you would normally operate it.
With a milivolt or IPI system, you would normally turn the main burner flame on and off with a wall switch where a standard system involves physically turning a knob or lever to turn the flame on and off (we will explain how each of these systems works later).
The difference between a millivolt or IPI system is whether you have a standing pilot light or not. Millivolt systems have a pilot light (that tiny little flame that runs constantly) and would normally have to be re-lit if it were to go out. IPI systems have no pilot light until you turn on your wall switch. With IPI, your pilot will electronically light itself after you flip on your wall switch. IPI is a relatively new system. You can also look at your rating place (see our What Type of Gas Fireplace Do I Have? page to see where to find your rating plate) and most often it will tell you what type of gas fireplace you have. The most common type of gas fireplace is a millivolt system.
How a Millivolt System Works
A millivolt system gets its power from the pilot light. The anatomy of a pilot light will look something like this:
To put it simply, the pilot light consists of three main parts.
- A Flame
- A Thermopile Sensor
- A Thermocouple Sensor
Most of the time gas fireplaces also have some sort of spark ignition system (piezo ignitor electrode as shown in the picture) to help assist you in relighting your pilot so you don’t have to light it with a match. The piezo ignitor is usually connected to a button that will create a spark when the button is depressed.
The pilot flame will heat up both the thermocouple and thermopile sensors. These sensors contain material that will create a small amount of voltage (under 1 volt) when they are heated up.
The thermocouple will create around 20-30 millivolts when enough heat is applied to it (.03 volts which is less that you can feel). This sensor is connected to the main control valve. This thermocouple will create enough electricity to keep the part of the gas valve open that controls gas flow to the pilot assembly. This is why the pilot will stay lit on its own after initially lighting the pilot and heating up the thermocouple. This is also why it will stop releasing gas if your pilot light goes out.
The thermopile is basically just a large thermocouple (actually a group of thermocouples inside a metal shell). But instead of creating 20-30 millivolts, it generates up to 900 millivolts. Although this seems like a lot, this is still under one volt of electricity (again not enough to even feel) but has enough power to open an electromagnet inside the main burner when you press your wall switch.