You turn the shower handle toward cold and the water stays hot. Or a kitchen faucet that used to mix normally now runs hot no matter where the lever sits. Stop using that fixture and keep children, older adults and anyone with reduced feeling in their hands or feet away from it. Don't check the water with a bare hand or keep working the handle to see if it changes. If someone has a serious burn, call 911 first; the plumbing can wait.
Only hot water is a symptom. It tells you hot and cold aren't reaching the outlet the way they should. It doesn't tell you which part failed, and it doesn't tell you whether anything violates code.
Is only hot water a code violation?
Not by itself. A code violation is a specific condition under the Massachusetts plumbing code, and your town's plumbing inspector decides whether permitted work meets it. Examples include missing temperature protection at a fixture that requires it, pipes connected the wrong way, or house pressure above the code limit with no regulating valve. A cartridge can also wear out in a faucet that was installed correctly.
The symptom tells you to stop and have it diagnosed; the diagnosis tells you whether a code problem is part of the story. That changes the repair. A worn part gets replaced, while an improper connection or missing protection may need a permitted correction and an inspection.
Start with where it happens
The most useful clue is how many fixtures are involved.
| Where you notice it | Possible causes to investigate | What we check first |
|---|---|---|
| One faucet or one shower | A worn cartridge, or a stuck pressure-balancing or thermostatic part inside that valve | The valve internals and the fixture's supply stops |
| Several fixtures on one branch | A shared mixing valve, a recirculation crossover valve, or a cold-side restriction on that branch | Which outlets are affected and what they share |
| Every fixture in the house | A cold-supply problem, a central mixing valve, or a recirculation fault near the water heater | Cold-water delivery and the equipment at the heater |
Timing helps too. Think back to whether it started after plumbing work, after a recirculation pump went in, or after the water was shut off for a repair. Tell us what you remember instead of recreating it.
How hot water ends up where cold should be
A crossover means heated water is getting into piping meant to carry cold. It takes two things: a path between the hot and cold sides, and a pressure difference that pushes water through it. Single-handle faucets and shower valves bring both supplies together inside the valve body, so a worn cartridge or failed seal can become that path. Other possibilities include a failed check valve in a mixing assembly, a recirculation crossover valve that is not closing as intended, or an incorrect piping connection.
Retrofit recirculation systems deserve a note of their own. Some use the cold line as a return, so brief warmth at the cold tap can be part of their operation. Persistent hot water needs investigation. Depending on the system, the cause can involve the timer, valve operation, installation or water-heater temperature. The system's manual and measurements guide that check; the symptom alone doesn't prove the valve has failed.
Where the water heater fits in
Do you need a hot water heater plumber, or is the problem in the faucet or shower valve itself? Where it happens gives clues, but the assessment still has to tell a cold-supply or mixing problem from a heater-control fault. It covers the heater, its connected piping and any mixing or recirculation equipment. Changing the thermostat does not diagnose the problem or repair a crossover, so leave adjustments to the person checking the system.
One pattern does point toward the heater: every hot tap is suddenly much hotter than usual while the cold side still runs cold. That can be a control problem. Stop using hot water, stay clear of the heater's relief valve if it is discharging, and call. Our water heater repair and replacement work comes in when testing points to the heater, its controls, or the valves and piping connected to it.
Scald safety has no single dial number
Storage temperature at the heater, the temperature leaving a mixing valve and the temperature at the showerhead are three different measurements. Massachusetts code specifies temperature-limiting controls for showers and other listed fixtures; the permitted arrangement depends on the application. The limits and exceptions are in 248 CMR 10.00, the state plumbing code. Reading the heater dial does not verify those protections, and the right heater setting also depends on the equipment and the people in the house.
Skin is a poor thermometer. A child or someone with limited feeling can be burned before they react, so leave the affected outlet off until it has been measured with an instrument.
High pressure is a separate problem
A pressure-reducing valve controls how hard water pushes through the house; it doesn't mix hot and cold. A mixing valve controls temperature; it doesn't regulate pressure. Pressure does play a part in a crossover, because the difference between the two sides drives water through the failed part. Lowering the whole house's pressure lowers both sides and leaves that path open.
Massachusetts code requires pressure reduction when pressure exceeds its limit, and adding a pressure-reducing valve means planning for the water heater's thermal expansion. If a house has both problems, each should appear as its own item in the repair scope, so you can see which fix addresses temperature and which addresses pressure.
What we check during a visit
We start by mapping the symptom: which fixtures, hot side or cold side, all the time or only sometimes, and whether recirculation or recent work is involved. We measure delivered temperature and pressure at selected points, then isolate components one at a time to find where hot and cold stop behaving. Those isolation steps are ours to do. Please don't close unfamiliar valves or open a mixing valve to test a theory; it can create a second problem and hide the first.
The repair follows the finding. A confirmed problem in a fixture's cartridge or valve internals fits faucet and shower valve repair. A recirculation or mixing problem gets the correction that testing supports, which may involve a setting, component or piping change. A wrong connection gets a permitted correction. We tell you which finding each item addresses and price approved work at a flat rate before anything starts.
Jeneral Plumbing is based in Westford, MA, and owner-operated by a Licensed Master Plumber (MA #9628831-PL-M). We serve homes within 20 miles across Middlesex & Worcester County and confirm the address, the work and availability before booking. A regular-hours visit carries an $80 dispatch fee — the cost of the visit, waived when you hire us for the work. Call (978) 392-7789 and tell us which fixtures run hot, whether the cold side is hot or missing, and when it started.
Questions homeowners and renters ask
Is only hot water an emergency?
Keep the affected fixture out of use and call for a prompt assessment. Whether a regular-hours visit is appropriate depends on the rest of the symptoms. If hot water suddenly becomes much hotter throughout the house, hot water discharges from the heater's relief outlet, or there is an uncontrolled leak or electrical danger, stay clear and seek immediate help. Do not plug a relief outlet or approach hot discharge. Call 911 for a serious burn or an immediate threat to life or safety. Our emergency plumbing page covers after-hours help. Off-hours, Sunday and holiday dispatch carries a separate $599 emergency callout fee. It is non-refundable and non-negotiable, collected prior to dispatch, covers the dispatch only and is never applied to repair work.
I rent. Who should I call?
Stop using the fixture and tell the owner or property manager in writing, through the building's normal repair channel. Owners should settle who can approve diagnosis and repair before the plumber arrives, so the visit doesn't stall waiting on a decision.
Written by Jeneral Plumbing.
This article was drafted with AI writing tools and edited before publication. AI tools did not inspect any job or validate technical conclusions.
Last updated .