Gas valves used in modern state of the art residential gas furnaces are typically controlled via a state of the art electronic ignition control or a printed circuit board. Other types of gas valves include the standing pilot gas valve. Gas valves can be found on gas furnaces, gas fired steam boilers or hot water boilers, and gas-fired water heaters. When troubleshooting a gas valve the technician should only be concerned with input to the gas valve and output of the gas valve. Whether it is an electronically or circuit board controlled gas valve or a standing pilot gas valve.
Gas Valve Troubleshooting | Electronic Ignition Gas Valve Troubleshooting
Gas Valve Troubleshooting | Basics
Any electronic component has a basic troubleshooting rule that every technician should follow when efficiently troubleshooting any electronic ignition gas component. The board should have an input and an output to follow a basic control sequence. The basic control sequence for an electronic ignition control board typically originates at a thermostat for a call for heat. By initiating a call for heat from the thermostat the technician begins the process of the sequence of operation. This completes a circuit to the main control. The electronic control or printed circuit board for the gas furnace. The control sequence of operation for a electronic ignition gas furnace will always include safeties to be proven before the gas electronic control board or printed circuit board allows any output to the gas valve. The safety circuit in many gas furnaces including boilers will include but are not limited to the following:
Components of the Furnace that Work in Conjunction with the Gas Valve
- Forced Draft or Induced Draft Pressure Switch
- Draft hood limit switches
- Limit switches in or near the heat exchanger
- Limit switches near the blower motor
- Any other safety switch that can be opened by temperature or pressure. A switch that is integral to the safety circuit of the gas furnace. Each brand of furnace is engineered differently. See the pictorial or the ladder diagram for all safeties engineered in the gas furnace. These diagrams can be found inside the control of the furnace.
Safeties | Gas Valve Troubleshooting
Once all the safeties are proven the electronic ignition control board will send a signal to the gas valve. The command will be to open either the main valve (if it is direct ignition) or to light the intermittent pilot light. Whether it is direct ignition or intermittent pilot light the flame must be proven through a flame sensor. Proven to keep the sequence from restarting and trying the ignition sequence again. If the flame cannot be proven then the system will shut down for a predetermined amount of time. +/- 4 hours is typical.
If a flame cannot be proven the manufacturer of the controls and the furnace do not want the gas furnace continuously trying for ignition. This is because a dangerous amount of gas can accumulate resulting in serious damage to a structure or people. If the flame is proven the sequence continues until the thermostat is satisfied and everything shuts down until the thermostat again calls for heat and then the whole sequences has to be proven over again so the furnace can provide heat.
Standing Pilot Gas Valve Troubleshooting
Everything that applies to the electronic ignition sequence of operation by the way of the safety circuit must be proven before the gas furnace will allow the gas valve to fire the main burners to provide heat. The difference is the standing pilot gas furnace always has a pilot light on.
Again, if you are not properly trained in the functionality of gas furnaces and basic safety practices you should call a professional. See our disclaimer. Working on HVAC equipment can be hazardous. Call a professional whenever your gas furnace is not working properly.
Gas Furnace Components – Gas Valve Troubleshooting
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