What It Is
Water heater sediment is mineral deposits - primarily calcium carbonate and magnesium carbonate - that settle out of the water supply and accumulate at the bottom of the tank over time. These minerals are dissolved in the incoming cold water and precipitate out as a solid when the water is heated. Every heating cycle deposits a small amount. Over several years, this layer can become several inches thick, creating a range of performance and durability problems for the heater.
What It Does
Sediment creates problems in several ways. First, it acts as an insulating layer between the water and the heat source. On gas heaters, the burner heats the tank bottom but must transfer that heat through the sediment layer to reach the water above - running longer and less efficiently. On electric heaters, the lower heating element can become encased in scale, causing it to overheat and eventually fail.
Second, sediment reduces the effective storage capacity of the tank. A tank with 3 inches of sediment at the bottom holds less usable hot water than it should, which can contribute to running out of hot water faster than expected.
Third, accumulated sediment can trap pockets of water beneath it. When the burner heats the tank, those trapped pockets vaporize and the steam escapes through the sediment layer with a popping, rumbling, or kettling sound. This is the most common cause of noise complaints on older water heaters.
Finally, heavy sediment buildup accelerates corrosion at the tank bottom and can clog the drain valve, making routine flushing impossible.
How It Works
The chemistry is straightforward: calcium bicarbonate and magnesium bicarbonate are soluble in cold water but become less soluble as temperature rises. When the water heater heats incoming cold water from roughly 50 degrees to 120 degrees, these minerals precipitate out of solution and fall to the bottom as fine white or off-white particles. Over time they harden into a concrete-like layer. The higher the mineral content of the local water supply, the faster sediment accumulates.
Common Problems or Signs of Failure
- Popping, rumbling, or kettling sounds during heating - steam escaping through the sediment layer
- Hot water runs out faster than it used to - sediment has displaced usable volume in the tank
- Higher energy bills - the heater runs longer to compensate for the insulating effect of the sediment layer
- Rusty or cloudy hot water - loose sediment particles or corrosion being stirred into the water supply
- Drain valve clogged or sluggish - sediment has packed around the valve opening
Can a Homeowner Check It?
You can get a good indication of sediment level by attaching a garden hose to the drain valve and draining a gallon or two into a bucket. If the water runs out brown, gritty, or cloudy rather than clear, significant sediment is present. You can also listen during the heating cycle - rhythmic popping or rumbling sounds are a reliable indicator.
- Listen during the water heater's heating cycle - popping or rumbling sounds indicate sediment
- Drain a gallon through the drain valve into a clear bucket and inspect the water
- Note whether hot water runs out faster than it did previously
- Check the age of the heater - most benefit from a flush within the first 2 years and annually thereafter in hard water areas
When to Call a Plumber
If the drain valve is clogged or the heater is making significant noise, a plumber can perform a proper flush and descale procedure, or evaluate whether the sediment buildup has reached the point where replacement is more practical than flushing. On heaters more than 8 to 10 years old with no maintenance history, flushing can sometimes dislodge enough scale to cause new leaks at already-stressed seams - a plumber can assess this risk before proceeding.
Related Plumbing Problems
- Why Is My Water Heater Making Noise?
- Why Does My Water Heater Run Out of Hot Water Fast?
- Why Is My Hot Water Rusty or Discolored?
Related Plumbing Terms
Related Gray's Services
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