A tankless water heater does all of its real work in one small part, the heat exchanger, a coil of narrow passages that water races through while the burner fires underneath. In plenty of places that part asks for very little attention. In Barstow it lives on desert-hard water, and hard water heated fast is exactly how scale gets made. Nothing about it is sudden. The unit gives up a little ground every week, and the first thing most people notice is a shower that cannot settle on a temperature.
What fast heat does to desert water
Barstow water arrives hard. It carries dissolved mineral picked up long before it reached the street, and as long as that water stays cold, the mineral rides along and goes down the drain with it. Heat changes the arrangement. When water gets hot quickly, part of that mineral comes out of solution and grabs onto the hottest surface it touches, and inside a tankless heater the hottest surface is the heat exchanger itself.
Older Barstow blocks add a second problem on top of the first. Many of those houses still run their original galvanized supply, and the old pipe concentrates what the water carries, so a heater on one of those houses collects rust flakes along with the scale. Both end up in the same place: the inlet screen and the exchanger passages, which were never wide to begin with. A tank heater can swallow a surprising amount of that debris before anyone hears about it. A tankless unit has far less room to hide it, which is why the first year on a new install tells us a lot about how the house will treat it.
Why a thin crust matters so much in a tankless
In an old tank heater, mineral mostly settles to the bottom as loose sediment. You hear it as popping and rumbling when the burner runs, and the tank keeps working for a long while in spite of it. A tankless heater does not get that grace period. The scale coats the walls of the passages instead of falling away from them.
That coating does two kinds of damage. It insulates the metal, so the burner has to fire harder and longer to push the same heat into the water, and the metal under the scale runs hotter than it was built to. It also narrows the passages, so less water gets through. The heater reads all of this through its sensors. When the outlet temperature swings or the exchanger gets too hot, a well-built unit shuts itself down to protect itself and throws an error code. Homeowners usually meet that code on a cold morning with soap in their hair, and by then the crust has been building for months.
Flushing is the job that keeps the unit alive
Descaling a tankless heater is a straightforward job when the unit was installed to allow it. Under a properly plumbed heater sit two service valves, one on the cold line in and one on the hot line out, each with a small port. We close the house off at those valves, hook a pump and hoses to the ports, and circulate a descaling solution through the exchanger until the crust breaks loose. Then the solution gets flushed out with clean water, and the inlet screen gets pulled and cleaned while we are there.
How often that needs to happen depends on the water and on how hard the house runs its hot side, so we set the interval from what we find inside the first time rather than from a number printed on a sticker. If your unit went in without service valves, adding them is the first thing we recommend, because a heater that cannot be flushed is a heater on a countdown. Our tankless installs in Barstow go in with those valves from day one.
The inline scale filter we plumb in
On Barstow installs we also put an inline scale filter on the cold line feeding the heater. It is a cartridge housing that treats the water on its way in so the mineral has a harder time bonding to hot metal. It does not soften the whole house, and it is not trying to. Its only job is protecting the one appliance that suffers most from scale, and it does that job quietly until the cartridge is spent and gets swapped.
A whole-house softener is a different machine with a bigger job. It pulls hardness out of the water for every tap, every fixture and every appliance downstream, and a softened house is easy on a tankless heater too. Some Barstow homeowners pair the two, some start with the filter and add a water softener later, and a few decide the filter alone is enough for how they live. If you are still weighing whether a tankless fits the house at all, our main tankless water heater installation page covers sizing and gas supply in more depth.
Signs your heater is already scaling
Scale announces itself in a handful of predictable ways. Hot water swings warm and cool in the middle of a shower even though nobody touched a faucet. Hot water takes longer to show up than it used to. The burner sounds louder or harsher than it did the first winter. The unit shuts off and posts an error code, and it clears after a restart only to come back a week later.
One comparison is worth making at the kitchen sink. Open the cold side all the way, then the hot. If cold runs strong and hot runs noticeably weaker, the restriction is likely on the heater side, and scale is a good suspect. If both sides are weak, the problem is upstream, often in old galvanized pipe that has been closing up from the inside for decades. When Kent called us about his twenty-year-old on-demand unit, Ruben “took the time to walk me through the current issues I was facing, and explained the different options available.” That is how we still run every one of these calls: look first, explain what we found, then talk about what to do.
Questions about tankless scale
Can I flush my tankless heater myself?
Some homeowners do, if the unit has service valves and they follow the manufacturer’s steps exactly. The gas and power have to be handled correctly, and the screen has to go back in right. If you would rather see it done once before trying it, we are glad to walk you through it on a service visit.
Does a softener mean I can skip the scale filter?
A softener treats hardness for the entire house, and a heater fed softened water scales far more slowly. Many households with a softener skip the separate filter. Others keep it as a second line of defense. A water test is the honest way to decide, since it tells you what you are actually dealing with.
Is it worth descaling an older unit that already throws codes?
Often it is, and a flush brings it right back. Sometimes the exchanger is blocked badly enough, or already leaking, that money spent descaling would be wasted. We open it up, tell you which situation you are in, and only then talk about a flush or a replacement.
Keep the exchanger clean
If your tankless has started acting moody, or you are planning one for a Barstow house and want it set up for the water it will actually see, call (877) 233-1033 or tell us about the unit. We run trucks all over Barstow 24 hours Monday through Saturday, and the flush, the filter or the new heater comes with a firm price you see before a single valve gets turned.