Change Water Heater San Mateo: What's Involved?

How do you know when it’s time to change it?

Age is the backstop, but the unit usually tells you first.

Rusty or discoloured hot water that clears when you run cold. That’s the tank, not the supply.

Rumbling or popping during a heating cycle. Sediment has settled on the bottom and water is boiling underneath it.

Moisture or staining at the base, even without an obvious drip. A tank that’s weeping is a tank that’s failing.

Recovery getting slower. If the second shower used to be fine and now isn’t, something has changed inside.

Repairs stacking up. Two service calls in a year on a ten-year-old unit is a signal, not a coincidence.

If you want the actual age rather than a guess, the serial number encodes the build date. The format differs by manufacturer — some lead with month and year, some with year and week, some use a letter for the year. Read the serial off the label to us over the phone and we’ll decode it in a few seconds.

For the decision itself — repair versus change, and what a new unit costs — see our guides to water heater repair in San Mateo and water heater replacement costs in San Mateo. This page is about the day itself.

What actually happens on the day

Isolate. Gas off at the appliance shutoff, or the breaker off for electric. Cold supply valve closed above the tank.

Drain. A hose onto the drain valve and out to a drain or the driveway. This is the slow part — a 50 gallon tank takes a while, and on an old unit the drain valve is often partly blocked with the same sediment that caused the problem.

Disconnect. Water unions, gas connector, and vent connector come apart. On electric, the circuit is disconnected and capped.

Remove. Even fully drained, a 50 gallon steel tank is awkward and heavy. This is where a clear path matters more than anything you could have done to help.

Set and level the new unit. Position gets decided by clearances, vent geometry, and combustion air — not by where the old one happened to sit. If the new tank is a different size, this step takes longer.

Reconnect, with new parts. New flex connectors, new shutoff, and a new earthquake-rated gas connector. We don’t reuse a twelve-year-old connector on a new heater.

Expansion tank. In San Mateo this is usually required, because Cal Water’s backflow preventer makes the home a closed system. If there’s an existing one, it gets tested rather than assumed.

Strap it. Two seismic straps, upper third and lower third, anchored into framing.

Pan and discharge. A drain pan with a routed line on interior or above-grade installs, plus the T&P discharge piped correctly.

Vent. Proper rise and slope on the connector, and a draft test once it’s running. On an atmospheric gas unit this is the step most likely to reveal that the old installation was never right.

Fill and purge. Tank fills, air bleeds out through a hot tap, then a full leak check at every joint.

Commission. Light it, set the thermostat — 120°F is the standard setting for scald protection and efficiency — and confirm it’s heating properly.

Haul away. Old unit leaves with us.

Then the part that isn’t on the truck: the inspection.

How long it takes, and how long you’re without hot water

For a like-for-like swap in an accessible garage: three to five hours on site. Add time if the unit is in a tight closet, if the size is changing, if venting needs correcting, or if the old install has surprises behind it.

Hot water timeline is longer than the visit. Count from when we shut the gas off to when the new tank is up to temperature — realistically five to seven hours for a gas unit, longer for electric, considerably longer for a heat pump.

Plan the day accordingly. Run the dishwasher the night before, not the morning of.

A heat pump conversion is a different animal and not a same-day job. It needs an electrical circuit, condensate drainage, and enough air volume around the unit, so it gets scheduled as a planned installation rather than a swap.

What to do before we arrive

Small things, but they take real time off the job:

• Clear a path from the door or driveway to the heater, wide enough to roll a tank through.
• Move stored items away from the unit. Garage installations in San Mateo are usually surrounded by boxes, bikes, and shelving.
• Clear the closet entirely if it’s an interior install.
• Know where your main water shutoff is, in case we need it.
• Secure pets, since the door will be open repeatedly.
• Leave space for the truck near the garage if you can.
• Decide on size or type beforehand. Switching from a 40 to a 50 gallon, or to a different fuel type, isn’t a mid-job decision — it changes what’s on the truck.

“responded quickly, explained everything clearly, and completed the job efficiently” — Google review, JK Plumbing customer

The inspection, and why the job isn’t finished when we drive away

Every water heater change in San Mateo needs a permit — including a direct like-for-like swap, and including an emergency replacement. There’s no exemption for urgency.

The process here is unusually painless: the City of San Mateo treats residential water heater replacement as an over-the-counter plumbing permit, approved while you wait, with no plans required for a replacement. It doesn’t hold up the work the way plan review would.

The inspector then checks the things on that list above that exist purely because code says so: strapping anchored into framing rather than drywall, T&P discharge routed correctly, vent connector rise and slope, the gas connector, the expansion tank, and the pan and drain line. Improper strapping is the most common failure.

Two reasons this matters to you beyond compliance. An unpermitted water heater surfaces during a home sale, where it becomes a negotiating point at the worst possible moment. And an insurer asking questions after water damage is a conversation you want to have with a permit in hand.

If a quote you’re comparing doesn’t mention a permit, that’s worth asking about directly.