Dirt leg
A capped vertical stub of pipe below the gas inlet tee that traps scale, dirt and liquid before they reach the gas valve.
Gas enters a tee and turns upward or sideways into the appliance, while debris and condensate fall straight down into the capped nipple below. The fuel gas code calls it a sediment trap and requires one ahead of most appliances. Inspectors and service techs look for it first, because a missing dirt leg is a common reason for gas valves that stick or leak through.
No dirt leg on the new boiler's gas line, inspector will red tag it, put a tee and a 3 inch nipple with a cap in there.
Also heard as
- drip leg
- sediment trap
Related terms
Gas train
The string of valves, regulator and switches that controls and safeguards gas on its way to the burner.
Burner
The assembly that mixes fuel with air and holds a stable flame to heat the boiler.
Nuisance trip
A safety shutdown or lockout caused by a faulty or marginal device, not by a real unsafe condition.