Short answer
Replace it if the tank shell is leaking, if it is over about ten years old and needs more than a minor part, or if the gas control valve fails on a tank past eight years. Repair it if it is under about eight years old and the fault is an element, thermostat, thermocouple, relief valve or dip tube. A dripping relief valve on a house with a pressure-reducing valve is usually thermal expansion, and the fix is an expansion tank, not a new water heater.
Key takeaways
- Water from the tank shell is the only water heater failure with no repair. Leaks from fittings, the relief valve or the drain valve usually are repairable.
- Under about eight years old, element, thermostat, thermocouple, relief valve and dip tube failures are worth repairing.
- A failed gas control valve can cost about half a new water heater; past eight years, that tips the decision to replacement.
- A relief valve that drips on a closed system is usually thermal expansion. An expansion tank fixes it and protects the next tank.
- Replacing a gas water heater in most of Montgomery County needs a WSSC Water permit, a WSSC-licensed master gasfitter and an inspection.
On this page
Most water heater calls start with one of three sentences: there is water under it, there is no hot water, or the hot water runs out. Each has an inexpensive answer and an expensive one, and the difference is almost always visible in the first twenty minutes — if someone looks before quoting.
This guide is how we make that call: find the actual source of the problem, weigh it against the tank’s age, and check the one pressure problem that destroys water heaters across WSSC-served houses. If replacement wins, it ends with how to use the moment well.
First: is the tank actually leaking?
Water on the floor is not automatically a failed tank. Trace it before anything else:
- The relief valve discharge pipe — the pipe running down the side of the tank from the valve near the top. Water here means the valve opened, usually from thermal expansion or excessive pressure. Repairable.
- Fittings above the tank — the cold inlet, hot outlet and their connectors. A weeping fitting runs down the jacket and pools at the base, looking exactly like a tank leak. Repairable.
- The drain valve near the bottom. Often a worn plastic valve. Repairable.
- A neighbour’s drain — an air conditioner or high-efficiency furnace condensate line, or a humidifier, in the same room. In summer this is a common false alarm. Not the water heater at all.
- The tank shell itself — water seeping from under the jacket or the bottom seam with everything above it dry. This one is not repairable.
If the tank is leaking now: close the cold water valve on the pipe entering the top of the tank. On a gas tank, turn the gas control knob to off; on an electric tank, switch off its breaker. If water is reaching finished space, connect a hose to the drain valve and run it to a floor drain — the water will be scalding, so keep hands and children clear. Then call.
Find the tank’s age
Age decides most of what follows, and it is on the rating plate. Most manufacturers encode the manufacture date in the serial number, but the format differs by brand. Look up your brand’s format, or send us a photo of the rating plate and we will read it. A tank that came with the house is often older than its owners think.
Symptom, cause and the usual call
| Symptom | Usual cause | Usual call |
|---|---|---|
| No hot water, gas | Pilot out: thermocouple or flame sensor; less often the gas control valve | Repair the thermocouple; a failed valve depends on age |
| No hot water, electric | Tripped high-limit, failed upper element or thermostat | Repair |
| Hot water runs out fast, electric | Failed lower element | Repair |
| Hot water runs out fast, gas | Sediment, or a broken dip tube mixing cold into the outlet | Flush, or replace the dip tube |
| Rumbling or popping | Sediment boiling under a layer on the tank bottom | Flush; if it has hardened on an older tank, plan replacement |
| Rotten-egg smell in hot water only | Bacteria reacting with a magnesium anode, common on well water | Repair: aluminum-zinc or powered anode |
| Rusty hot water | Anode used up, tank lining corroding | Anode if caught early; replace an older tank |
| Relief valve dripping | Thermal expansion or excessive water pressure | Expansion tank or pressure-reducing valve; replace the relief valve if faulty |
| Water from the tank shell | Tank rusted through | Replace |
Gas tanks also get a draft and carbon monoxide check on every visit. A pilot that keeps going out can be a blocked or orphaned flue, not a bad part — our guide to power vent vs. atmospheric water heaters explains why that is so common in older Montgomery County houses.
Age against the cost of the repair
| Tank age | Minor part (element, thermostat, thermocouple, relief valve, dip tube) | Gas control valve | Tank shell leak |
|---|---|---|---|
| Under 8 years | Repair | Usually repair; check the tank warranty | Replace; check the tank warranty first |
| 8 to 12 years | Repair if the tank is otherwise sound | Replace | Replace |
| Over 12 years | Usually replace | Replace | Replace |
The gas control valve is the pivot. It is the most expensive common part, often around half the price of a new water heater, so on any tank past eight years it moves the decision to replacement. Residential tanks commonly carry a six-year tank warranty, longer on premium models; a shell leak inside that window is worth a call to the manufacturer before you pay for a new unit.
The WSSC pressure problem that kills tanks early
This is the repair we make most often that people have never heard of.
Water expands when it is heated. In an open system that extra volume pushes back out into the water main. But many Montgomery County houses are closed systems: a pressure-reducing valve, check valve or backflow preventer on the incoming service stops water flowing back out. Every heating cycle then pushes the house pressure up until the relief valve opens. The valve drips, the tank and every fixture take a pressure spike several times a day, and the tank fails years early.
The plumbing code addresses both halves. The International Plumbing Code — which WSSC adopts, with local amendments — requires a pressure-reducing valve where static pressure exceeds 80 psi (Section 604.8) and thermal expansion control on any storage water heater fed through a check valve, pressure-reducing valve or backflow preventer (Section 607.3). Parts of Silver Spring run high enough pressure to need the reducing valve, which in turn makes the house a closed system that needs the expansion tank.
The test takes a few minutes: a gauge on a hose bib shows static pressure, and leaving it on through a heating cycle shows the spike. If your relief valve drips and you have no expansion tank, adding one is the repair — and it protects the next tank as well as this one.
Well water: Olney and outer Potomac
Private wells change the repair profile. On untreated well water in Olney and Potomac, anodes are consumed far faster than on WSSC water, sediment fills the bottom of a tank in a few years, and sulfur odor is common. Three habits make the difference between an eight-year tank and a twelve-year one:
- flush the tank every year, before sediment hardens;
- inspect the anode every few years and replace it before it is gone;
- use an aluminum-zinc or powered anode where sulfur odor appears.
Tankless units on well water need descaling about twice a year; a tankless repair call for “lost output” is very often a unit that has never been descaled.
If you replace, use the moment
An emergency replacement tends to put the same tank back in the same place. A planned one is the one chance in a decade to change type, and a few questions are worth answering first:
- Gas or no gas? If you have an electric tank or no gas service, a heat pump water heater usually wins on running cost — see heat pump vs. gas.
- Do you run out? If the household regularly drains the tank, compare a larger tank against tankless — see tank vs. tankless.
- Is the vent still right? If the furnace has been upgraded, the water heater may be orphaned in the chimney.
Whatever the type, size it by the right number. The U.S. Department of Energy’s guide to selecting a new water heater recommends choosing a storage tank whose first-hour rating matches your household’s peak-hour demand within a gallon or two. Tank gallons alone do not tell you that.
If a tank fails without warning and you have not decided, a same-day like-for-like replacement is a reasonable bridge. It is better to decide now, while it still works.
Permits and who can do the work
In Montgomery County outside Rockville and Gaithersburg, replacing a water heater is regulated by WSSC Water. WSSC’s guidance for homeowners is that gas water heater replacement must be done by a WSSC-licensed master plumber or gasfitter under a WSSC Water permit, with a WSSC inspection after installation; homeowners may not install gas appliances themselves. Ask for the license number and check it.
That check matters. The county’s Office of Consumer Protection has warned residents about unlicensed plumbers working under licenses borrowed from master plumbers for a fee. An unpermitted water heater is also a standard item on a home inspection report when you sell.
How we handle it
A water heater repair visit from us traces the water or the fault first, checks pressure, expansion control, draft and the anode, and then gives you the repair price and the replacement price together, in writing. If you choose to replace within 30 days, the diagnostic fee goes toward the installation. Tell us what the tank is doing and how old it is — a photo of the rating plate helps.
Sources
- Selecting a New Water Heater U.S. Department of Energy, Energy Saver Choosing by fuel, type and first-hour rating; matching first-hour rating to peak-hour demand.
- Information for Homeowners WSSC Water Licensed master plumber or gasfitter, WSSC permit and inspection requirements for water heater replacement.
- Plumbing/Gasfitting Licensing and Inspections Montgomery County Office of Consumer Protection WSSC licensing in the county, separate licensing in Rockville and Gaithersburg, and warnings about unlicensed plumbers using borrowed credentials.