Water Not Hot Enough
Updated February 20, 2026
Warm but not hot enough -- different from no hot water. Heater is working but something prevents it from reaching or holding temperature. Thermostat too low, sediment insulating the element, failing element, or undersized unit.
Overview
Producing heat but not enough. Most common: thermostat set too low -- factory default 120 may not be sufficient, especially in cold months when incoming water is colder. Second: sediment insulating the bottom from the heat source. Beyond those easy fixes: failed lower element (electric), broken dip tube, or undersized for demand. Simplest to most involved.
Symptoms
- Lukewarm but not truly hot -- heater is doing something but temperature is noticeably low
- Runs out faster than it used to -- less shower time before it goes cold
- Varies by time of day -- hotter in the morning, cooler during peak usage
- Some fixtures hot, others lukewarm -- distant fixtures lose heat in the pipes
- Popping, rumbling, or crackling from the heater -- sediment buildup
- Gradually decreased over months or years -- sediment accumulation or slowly failing element
Common Causes
- Thermostat too low -- gas: dial on the control valve. Electric: two thermostats behind access panels. Below 120 or accidentally bumped. 120 for most, 125-130 for hotter preference.
- Sediment insulating the heat source -- minerals settle on the bottom. Gas: insulates from the burner. Electric: covers the lower element. Reduces effective capacity by several gallons.
- Failed lower element (electric) -- lower does most of the work. Burns out or shorts, upper alone cannot maintain temperature. Some hot water from the top, runs out fast.
- Broken dip tube -- directs cold water to the bottom. Cracks or breaks, cold enters at the top and mixes with hot. Especially common with mid-1990s defective polypropylene tubes.
- Undersized -- household grew since installation. 40-gallon: 2-3 people. 50-gallon: 3-4. Dishwasher during shower time overwhelms smaller tanks.
- Long pipe runs -- heater far from fixtures, heat lost in uninsulated pipes. Not a heater problem but affects perceived temperature.
What You'll Need
How to Fix It
-
Check and Adjust the Thermostat
Gas: dial on the control valve, turn to desired setting (120 recommended). Electric: breaker off, access panels off, insulation back, flathead screwdriver to adjust both thermostats to the same temp. Panels back on, power on, wait 1-2 hours, test.
Tip: Cooking thermometer at the closest tap. Run hot 2-3 minutes before measuring. Compare to the thermostat setting. -
Flush the Water Heater Tank
Power off, cold supply off. Garden hose on drain valve to a floor drain or outside. Drain completely -- discolored water, sediment particles. Open cold supply briefly to stir and flush remaining. Repeat until clear. Close, refill, power on, test after 1-2 hours.
Warning: Water is hot. Cool for hours or handle carefully. Do not stand in front of the drain valve -- sediment causes intermittent spurts. -
Test the Heating Elements (Electric Water Heaters)
Thermostat and flushing did not fix it? Test elements. Breaker off, panels off. Multimeter on continuity/resistance. Disconnect one wire, probes on the two terminal screws. Working: 10-20 ohms. No continuity: burned out. Also test grounded: probe to terminal and metal tank. Any continuity means shorted to ground, must replace.
Tip: Lower fails more often -- closer to sediment at the bottom. Sediment covering it causes overheating and premature burnout. -
Replace a Failed Heating Element
Breaker off, cold supply off. Drain below the element level. Element wrench (1-1/2 inch socket) to unscrew. Take old one to match wattage and type. Teflon tape on threads, screw in, tighten. Reconnect wires, refill, check for leaks, power on.
Warning: Never power on with empty or partial tank. Elements must be submerged or they burn out in minutes. Open a hot tap, wait for steady stream with no air, then restore power. -
Check the Dip Tube
White plastic particles clogging aerators? Dip tube deteriorated. Water and power off. Disconnect cold supply, pipe wrench on the inlet nipple, pull dip tube straight up. Cracked, broken, crumbling? Replace with cross-linked PEX (more durable than original polypropylene). Insert, reconnect, restore.
Tip: Dip tube disintegrated? Plastic fragments clogging aerators, shower heads, and screens everywhere. Flush all faucets and clean aerators after replacing. -
Address Pipe Heat Loss and Capacity Issues
Hot at the tank but lukewarm at distant fixtures? Heat loss. Foam insulation on all accessible hot water pipes ($1-3 per 6-foot length). First 6 feet from the heater and any unheated spaces are priority. Running out during high demand? Larger tank or tankless.
Tip: Thermostatic mixing valve at the heater outlet. Tank at 140 for faster recovery, valve blends to safe 120 at fixtures. Effectively increases usable capacity.
When to Call a Pro
Call a plumber if not comfortable with electrical element work, if the dip tube has disintegrated, if the heater is undersized and you want sizing advice, if considering tankless (different venting, potentially upgraded gas or electrical), or if the gas burner fires but still does not heat adequately.
Prevention Tips
- Flush annually. Single most important task for efficiency and lifespan.
- Check thermostat at the start of winter. Incoming water is colder -- may need 5-10 degrees higher.
- Insulate hot water pipes. First 6 feet from the heater and unheated spaces. Cheap, significant heat loss reduction.
- Electric heater? Test both elements during annual maintenance. Failing element reduces capacity before full failure.
- High demand household? Timer for off-peak heating, or mixing valve for higher tank temp with safe delivery.
- Replacing? Size for actual usage. Plumber calculates first-hour rating based on people and fixtures.