Gas valve replacement on a water heater

Two different parts get called the gas valve. One is the shutoff on the pipe, a lever or knob you can turn by hand. The other is the control valve bolted to the tank, which meters gas to the burner on the thermostat's orders. This page is about swapping the second one, a job Fixr prices at $150 to $300. For the full list of fixes, go to the water heater repair page.

Which gas valve are we talking about?

The manual valve sits on the supply pipe a short distance from the heater and exists to cut gas off for service. The gas control, by contrast, hangs low on the tank, carries the temperature dial and often the pilot controls, and opens and closes the burner supply automatically. Only the second kind is "replaced" when a heater fails to heat.

If someone mentions a replacement of the manual valve, that is a different, smaller task: a new quarter-turn shutoff on the line. For earthquake protection there is a third device again, the automatic seismic shutoff at the meter or on the house line, explained in a separate seismic valve page.

Which signs say the control valve has failed?

Typical signs: a pilot that burns while the main burner never ignites, the dial turns without any effect on the water temperature, the burner will not shut off when the tank is hot, or you can smell gas around the control. A stuck or leaking valve rarely looks like anything else.

The thermocouple is the cheaper suspect, and a plumber normally eliminates it first. If the pilot stays lit with a fresh sensor yet nothing happens, attention moves to the control. Leaving the burner on past the set temperature is worse: that is a safety fault, so the unit stays off until someone has looked at it.

Detect gas near the heater? Walk everyone out, touching no light switches. In the open air, report it to the utility on its listed line, 1-800-427-2200, and use 911 when people are in danger.

What does a new gas control cost, and when is the heater the better buy?

Fixr's national band for a gas valve swap is $150 to $300 including labor, inside an overall heater repair band of $150 to $750. Controls are often specific to one brand and model, so parts can be slow to arrive for older units. Rheem's rule is to replace instead once the repair bill passes 50 percent of a new heater's price.

Age decides most cases. A control on a heater that is 4 or 5 years old is a sensible repair. That same bill on a tank beyond its tenth year, rusting at the base or rumbling with sediment, usually argues for a new unit; see replacement cost and how long a tank lasts. These prices are national averages; the estimate in writing is what counts.

Why is this work off limits for a weekend handyman?

Because it opens a gas appliance. The state contractor board's plumbing classification, C-36, includes gas piping, gas appliances and their connections, and a mistake with a control means a leak, a flame problem or carbon monoxide. Manufacturer instructions generally say only trained people should service gas controls.

California's licensing rules reach paid work once labor and parts total $1,000, plus every job that requires a permit. A control swap may fall under that amount, but safety is the main reason to hire someone. You can start a visit request on the quote page.

What takes place during the visit?

Expect the plumber to confirm the diagnosis first, close the gas, remove the old control, install its replacement with new seals, then check every joint for leaks, relight the pilot and test the burner, flame and venting. Safety checks usually take as long as the swap.

When the heater has nearly run its course, expect an honest conversation about the tank too. A plumber who sees a corroded base, a missing relief valve discharge pipe, or no earthquake straps may suggest changes. Strapping is a legal requirement, found in section 19211 of the state health and safety statutes, and a replacement heater needs a city permit; check with your Building Division.

What makes a gas control fail in the first place?

Age is the main cause, plus sediment that makes the burner cycle harder, soot, moisture around the control and the gradual wear of seals and thermostat parts. Hard water is a contributor in Anaheim, where the city reports about 18 grains per gallon: more scale on the tank bottom means longer burn times.

Flushing the tank on the schedule the manufacturer gives and replacing the anode rod when it is spent both ease the load. Neither stops a control from wearing out, but a tank kept clean tends to run cooler at the base and keep its burner chamber cleaner. Related reading covers swapping the anode rod and a worn pilot sensor.