No Hot Water Service Call
Purpose
"No hot water" is the most-dispatched water heater call and the one most often closed with a part that was working. The tank gets condemned because it is the biggest object in the room, when the fault was a supply the tech never proved, a crossover in a shower valve two floors up, or a safety device that opened for a reason nobody looked for. This procedure forces three things before a part is named: the complaint measured at a fixture, the appliance proved to be fed, and the cause of any tripped safety device established rather than reset away.
Scope
Covers the diagnostic visit on a residential or small-commercial storage or tankless water heater, gas or electric, where the customer reports no hot water, not enough, or lukewarm.
It does not cover the emergency arrival gates in detail: a gas odor goes to the gas odor call response SOP, a burst line goes to the burst pipe emergency response SOP, and a sewage or flooding hazard goes to its own procedure. Annual service, descaling and the changeout day are their own SOPs and this procedure hands off to them rather than repeating them.
Roles and the handoff
| Role | Owns | Hands off |
|---|---|---|
| Office | Asks fuel, age, whether anything else in the house changed, and whether water is on the floor | Warns the tech of a reported smell or standing water before dispatch, not on arrival |
| Service tech | Every step below, including the refusal to reset a safety device blind | Returns the measured fixture temperature, the supply proof and the cause found |
| Owner or lead | The replace-or-repair call on an aged tank | Puts the reason in the quote, so the customer is not choosing on age alone |
The handoff that breaks: the tech resets a tripped high limit, hot water returns, the ticket closes, and the same customer calls back in nine days. A reset with no cause written down is an unfinished visit.
Procedure
Run the arrival gates at the door before any diagnosis, because two of them mean you do not enter. If anyone smells gas, everyone leaves the building immediately, nothing is switched on or off, no lights, no phone used inside, and the call to the gas utility and the shop is made from outside; that call then belongs to the gas odor SOP. If there is standing water touching an electric appliance or its circuit, nobody touches the appliance or metal in contact with it, and the branch circuit is opened from a dry location. Acceptance: both gates cleared and stated on the ticket. Wrong looks like entering to "just take a look": stop at the threshold. Hazard: these gates are the hazard, and each carries its own action above.
Measure the complaint at a fixture before you look at the appliance. Run the nearest hot tap for two minutes and read it with a thermometer, then repeat at a fixture on another branch. Acceptance: two recorded temperatures and the complaint classified as no hot at all, hot that runs out early, or lukewarm everywhere. Wrong looks like taking the customer's word and going straight to the tank: "runs out early" is a sizing, dip tube or recirculation problem, and "lukewarm everywhere" is usually a crossover, and neither is diagnosed at the appliance. Hazard: water at an unknown temperature can arrive scalding, so open the tap slowly with your hand out of the stream.
Prove the appliance is being fed before you condemn anything inside it. On gas, confirm the appliance shutoff is open and read manifold or inlet pressure at the control's test port with a manometer against the rating plate figure. On electric, confirm the breaker is closed and read voltage at the appliance disconnect or junction. Acceptance: fuel or voltage present at the appliance's own connection, recorded as a number. Wrong looks like a tripped breaker reset with no reason found, or a gas cock somebody closed during other work: find why before you restore it. Hazard: a live reading is energized work under 29 CFR 1910.333(b)(2) by a qualified person per 1910.332 and 1910.399, and where the reading is not needed to decide, take the appliance dead instead.
On an electric unit, de-energize, prove dead, then read the safety device and the thermostats before touching an element. Open the breaker and verify at the element terminals with a meter proved on a known live source before and after, per NFPA 70E-2021, 120.5. Then check the high limit, called the ECO, whose trip temperature is marked on the part and commonly sits near 180 F on residential stock, and ohm each element: a 4,500 W element on 240 V should read close to 240 squared divided by 4,500, which is 12.8 ohms, and any reading to the tank shell is a failed element. Acceptance: ECO closed, each element within about 10 percent of its calculated resistance, thermostats switching with the dial. Wrong looks like an open ECO: do not reset it, establish why it opened, because a welded thermostat that cooked the tank will do it again with a new part on the invoice. Hazard: capacitive and stored charge is not the issue here, an unproven circuit is, so the proving sequence above is not optional shorthand.
On a gas unit, watch a full ignition sequence, then prove the appliance vents and does not leak before anything is left lit. Acceptance: pilot or igniter proves, main burner lights and stays lit through a full call, no leak on a soap or electronic check at every joint you disturbed, and no spillage at the draft hood on a smoke or match test about a minute after the burner fires. Wrong looks like a burner that lights and drops out: that is a flame-sense or thermocouple path, not a tank, and it is a repair. Hazard: wear a personal carbon monoxide monitor for the whole visit and leave the appliance off and red-tagged if spillage persists, because a heater that will not vent is a hazard to the household, not an inconvenience.
On a tankless unit, read the code and the flow before you read anything else. Acceptance: any stored fault code recorded and looked up in that model's manual, activation flow confirmed by running a fixture and watching the unit fire, and gas supply verified under step 3 at full fire rather than at idle. Wrong looks like a unit that will not fire on a trickle draw: many models need a minimum flow to activate, so a low-flow aerator or a partly closed isolation valve reads as a dead heater. Where scale is indicated, hand off to the descaling SOP rather than working it here. Hazard: a tankless at full fire draws far more gas than a tank, so an undersized line shows up here first and is a combustion problem, not a plumbing preference.
Where the complaint is lukewarm everywhere and the appliance is making hot water, hunt the crossover. Close the water heater's cold inlet, open a hot tap and watch: on a sound system flow stops within seconds. Acceptance: no continuing flow at the hot tap with the inlet closed. Wrong looks like flow that keeps running, which means cold is entering the hot side through a failed single-lever cartridge, a mixing valve, or a recirculation crossover fitting: isolate fixtures one at a time until it stops. Hazard: you are working with a tank still at temperature, so bleed pressure at a low fixture rather than cracking a fitting at the tank.
Restore the appliance and verify the protective function you disturbed still works. Close the breaker or open the gas cock, stand to the hinge side of the panel rather than square in front, and run a full recovery. Acceptance: on electric, the thermostat cuts out at its setting so the tank never approaches the ECO's marked trip temperature, and the fixture reads within about 5 F of target; on gas, the burner cycles off on the control and the spillage test repeats clean at the end of the cycle. Wrong looks like heat returning with no cutout observed: stay for the cycle, because the reset you did is only proved by the cutout you watched. Hazard: this step puts fuel or electrical energy back with the customer in the house, so clear people from the room, confirm covers are on, and keep the carbon monoxide monitor on you through the gas cycle.
When the visit does not resolve
Tank is leaking from the shell: this stops being a repair, and it goes to the failure investigation and warranty claim SOP before anything is removed. Cause of an opened safety device cannot be established: leave it open, red-tag the appliance, and quote the diagnostic return, because a device that opened for an unknown reason is doing its job. Customer declines the repair on an aged tank: record the decline and the condition found, and do not leave a heater lit that failed a spillage test. Nobody on site is qualified for the electrical reading: the electrical portion waits for someone who is, and the ticket says so.
The record this produces
- Both arrival gates, cleared or invoked
- Two fixture temperatures with the branch each was taken on, and the complaint class
- The supply proof as a number: manifold or inlet pressure against the plate, or voltage at the disconnect
- Element resistances against the calculated value, ECO state and its marked trip temperature, thermostat behavior
- Gas: ignition sequence observed, leak check result, spillage test result and the time after firing
- The cause established for any tripped device, in one plain sentence
- The cutout observed at the end of the visit, with the fixture temperature
The line that earns its keep is the cause sentence. Without it the next tech cannot tell a solved call from a reset one.
Worked pass: 40 gallon electric, no hot water at all
Nine year old electric tank in a basement, no water on the floor, no odor. Dial set to 120 F.
- Step 1: both gates clear, stated on the ticket.
- Step 2: kitchen tap 61 F after two minutes, upstairs bath 60 F. Cold-in-the-pipes cold, so the class is no hot at all.
- Step 3: breaker closed, 241 V at the appliance junction. The appliance is fed, so the fault is inside it.
- Step 4: FAILED, and the stop rule held. Breaker opened, meter proved live on a known source, 0 V at both element terminals, meter proved live again. ECO found open, marked 180 F. Elements ohm out at 12.7 and 12.8 against the 12.8 the plate implies, so both are serviceable and neither reads to the shell. Upper thermostat reads continuity with the tank standing at 61 F and the dial well below that, which is a welded contact. Not reset. Cause recorded: the upper thermostat failed closed, drove the tank past 180 F and the ECO did exactly what it exists to do.
- Step 5 and 6: not applicable, electric tank.
- Step 7: not run, the complaint is no hot at all rather than lukewarm.
- Step 8: combined upper thermostat and ECO replaced as one part, breaker closed from the hinge side, full recovery watched. Upper stat cut out with the tank at 122 F against the 120 F dial, so the tank never came near the 180 F trip. Kitchen tap read 118 F, which is 2 F under the 120 F target and inside the 5 F band.
If step 4 had been a reset, the customer would have had hot water that afternoon and the same open ECO inside two weeks, with a second dispatch and no better information than the first one produced.
References
- Manufacturer service manual and rating plate for the specific model, for element wattage, ECO trip temperature and manifold pressure
- NFPA 70E-2021, 120.5 for the proved-before-and-after sequence, with 29 CFR 1910.333(b)(2), 1910.332 and 1910.399 for practices and who may take a live reading
- National Fuel Gas Code, NFPA 54 / ANSI Z223.1, in the edition your authority having jurisdiction has adopted, for gas piping and appliance connection practice
- See related: the gas odor call response SOP, the tankless descaling service SOP, the water heater annual service SOP, and the water heater failure investigation and warranty claim SOP