Start with the boring causes: power to an electric heater has dropped, a gas pilot has gone out, or the tank has simply emptied after a long run of showers. Those three account for most cold-tap mornings. Which one fits you depends on the label on the heater, so find that first. A gas smell, standing water or a tripped safety limit means stopping the checks and handing over. The water heater repair page explains the way a local plumber is arranged across Santa Monica and the Westside.
What are the usual reasons the hot tap runs cold?
The usual causes are lost power or a tripped breaker on an electric tank, an extinguished pilot or failed thermocouple on a gas tank, a failed heating element, a thermostat set too low, or a tank that has run out after heavy use. Sediment, a closed valve and a failed tankless igniter are the next suspects.
A quick split helps. If hot water is merely lukewarm, an element or thermostat is likelier. If you get nothing at all, think power, pilot or a closed valve. If hot water vanishes after ten minutes in the shower, the tank is undersized for the household or the lower element has quit. Hot at one tap and cold at another often points at a mixing valve or crossover fault in that fixture, not at the heater.
How do I troubleshoot an electric tank?
Breaker first, reset button second, thermostat third. That is the order in Rheem's manuals: confirm the circuit has power, reset the high-temperature cutout if it tripped, and make sure the thermostat is not set too low. If it trips again, a plumber takes over.
Switch the breaker off before opening any access panel. The reset is a red button above the upper element, under a cover and insulation, and it trips when the water gets too hot. Pressing it restores power, but the maker says a qualified person should find out why it overheated. If one or both elements have failed, the manual points to service. Work behind that panel is not casual, and Rheem itself says anything with electrical risk belongs with a plumber.
Owners of a Rheem or a similar tank can read the longer Rheem electric water heater repair piece on element and thermostat checks, and replacing a heating element for the part itself.
What do I look for on a gas tank?
Check the pilot flame or the status light, then sniff near the base of the heater. A smell means no switch and no lighter: the manuals from A.O. Smith and from Bradford White both say to get out, phone the gas supplier, and hold off until the leak is fixed. No smell means the lighting label on the heater is your script.
Gas heaters differ. On a model with an igniter, the label has you turn the knob to off, wait about ten minutes for any gas to clear, then follow the pilot steps. When it will not stay lit after the attempts the label allows, the manuals tell you to stop and book service. Likely culprits include a worn thermocouple or thermopile, a dirty pilot tube, or air in the gas line after a shutoff. A tripped earthquake valve causes the same symptom. Further reading: pilot light repair and gas water heater repair. For a gas smell the utility's line is 1-800-427-2200, with 911 first when anyone is hurt.
Why is my tankless heater giving cold water?
A tankless unit fires only on demand and shuts itself down on a fault, so cold water often traces to an error code, a clogged filter, scale, weak flow, a vent problem or a missing gas or power supply. The display code and the manual tell you which. Flow below the minimum can also make the burner stay off.
Scale builds up inside these units where water is hard, and the maker's manual sets the descaling interval, so have the plumber read the yearly water quality report from your supplier alongside you. A code that survives one restart is a service call. Thinking of moving from tank to tankless? The tank versus tankless comparison is the place to begin.
Is a cold shower an emergency?
Usually not. Cold water alone is an inconvenience. Water leaking from the tank, a gas smell, a scorched smell or sparking at an electric heater turn it into an emergency. Without those four, wait for a regular visit, which also costs less than an after-hours call.
A leaking tank needs its cold supply valve shut, its power cut at the breaker (or its gas control turned to the pilot or off setting), and a phone call. Do not wade into water around an electric unit. Fast leaks have their own page, emergency water heater repair.
What if I rent an apartment with cold taps?
Send the landlord or manager a dated note about the problem, and keep a copy. Under California's habitability rules (Civil Code 1941.1), working hot and cold water belongs in any livable rental, which makes it the landlord's repair, not yours. Leave a shared heater closet alone.
Many Westside apartments run on a central boiler or a shared heater, in which case nothing in your unit will fix it. If days go by without action, the page on apartment hot water laws lays out tenant options. A plumber can still diagnose a shared system once the landlord hires one.
What if it is a boiler?
Where hot water comes from a boiler or an indirect tank, read the boiler's display and the thermostat call before anything else. Boilers lock out for safety, and the manual describes a single reset. Lockouts that repeat mean a fault for a plumber, not another reset.
Gas boilers follow the same safety rule as any gas appliance. Older homes in Santa Monica may still have these systems, and parts for them can be harder to find, so raise the question early.
Common questions
At what point should I pick up the phone?
Call if the breaker or pilot checks changed nothing and the heater is still cold an hour or two later. Leaks and gas smells do not get that wait. A plumber can often diagnose in one visit, though the repair itself may wait on a part.
Who fixes a cold-water problem?
A plumber, since water heaters belong to the plumbing trade, gas and venting connections included. Tenants call the landlord first. A gas smell goes to the utility ahead of anyone else. To arrange a local plumber for an owned home, use the quote page.
What explains a cold Rheem tank?
Rheem's electric manuals blame power loss, a tripped high-temperature cutout, a low thermostat or failed elements. Check the breaker, press the red reset with the power off, and read the control display. If it trips a second time, stop there and call, because something is running too hot.
Does a failed heater always mean a new one?
No. An element, thermostat, thermocouple or igniter is a fraction of the price of a new tank, and a plumber can usually swap one in a single visit. A shell that leaks cannot be fixed, though, and older tanks may not justify repair. The water heater replacement cost article covers prices and when repair stops making sense.
The rest of our guides start from Sunset Coast Plumbing plumber.
Sources used
Page updated