HVAC Error Code G2 — What It Means & How to Fix It

What Does This Error Mean?

G2 on an HVAC system indicates a gas pressure fault. The system detected that the gas supply pressure is outside the acceptable range — either too low to maintain a stable flame, or the pressure switch detected a problem with the gas supply circuit. This is a safety lockout that requires professional diagnosis.

Affected Models

Gas furnaces
Gas boilers
Gas combination HVAC systems

Common Causes

The gas supply pressure from the utility or regulator is too low to sustain proper combustion
The gas pressure switch inside the furnace has failed or is stuck in the open position
The gas valve is not opening fully, restricting gas flow and causing low manifold pressure
A partial blockage in the gas line is reducing the pressure reaching the furnace
The pressure switch tubing has a crack or disconnected fitting, causing a false pressure reading

How to Fix It

Check that the gas supply valve is fully open. The manual shutoff valve on the gas line feeding the furnace should have its handle parallel to the pipe (open) — not perpendicular (closed).

A partially closed valve reduces gas flow and can trigger G2.
Check if other gas appliances are working. Try the gas stove or water heater. If none are working, the main gas supply to your home has been interrupted. Contact your gas utility.

A main gas supply interruption affects all appliances at once. The HVAC system is not at fault in this case.
Inspect the pressure switch tubing. With the system powered off, locate the small rubber or plastic tube connected to the pressure switch. Check for cracks, kinks, or disconnected ends. Reconnect or replace if damaged.

The pressure switch senses gas pressure through this small tube. A damaged tube gives incorrect readings and triggers G2 even when the gas supply is normal.
Reset the system. After checking the above items, turn the system off at the thermostat and circuit breaker, wait 5 minutes, then turn it back on. Some pressure switch trips clear after a manual reset.

Do not reset repeatedly without identifying the cause. Multiple unsuccessful ignition attempts can be a safety hazard.
Call a licensed HVAC technician. The technician can use a manometer to measure actual gas pressure, test the pressure switch, and adjust the regulator if needed.

Gas pressure testing requires a manometer — a device that most homeowners do not have. This is the step that requires professional service.

When to Call a Professional

Gas pressure problems require a licensed HVAC or gas technician. Gas pressure testing and adjustment require specialized instruments and training. Do not attempt to adjust the gas valve or regulator yourself — incorrect pressure settings cause dangerous combustion conditions. Call a professional for any G2 error that does not clear after checking the simple items below.

Frequently Asked Questions

How do I know if my gas pressure is too low?

You typically cannot tell without measuring instruments. Symptoms of low gas pressure include: the furnace starting then shutting off quickly, the flame appearing yellow instead of blue, or the system running but not heating adequately. A licensed technician can measure inlet and manifold pressure with a manometer to confirm.

Can cold weather affect gas pressure?

Yes. Extremely cold temperatures can affect the pressure in propane tanks — the liquid propane contracts and produces less vapor pressure. Natural gas supply from the utility is regulated and generally consistent, but extreme demand on cold nights can sometimes cause brief pressure drops. If G2 appears only on the coldest nights, low propane tank level or utility pressure issues are possible causes.

What is the correct gas pressure for a residential furnace?

Standard natural gas inlet pressure for a residential furnace is 5 to 7 inches WC (water column). Manifold pressure (after the valve) is typically 3.5 inches WC for natural gas. Propane (LP) systems use higher pressures — typically 11 inches WC inlet and 10 inches WC manifold. Only a licensed technician with a manometer should measure and adjust these values.