Tankless water heaters are pretty amazing. They give you hot water whenever you need it without storing gallons of water in a big tank. But like any appliance, they can have problems. Understanding common tankless water heater problems helps you spot issues early and fix them before they get worse. In this guide, we’ll walk through the five most common tankless water heater problems homeowners face and show you how to solve them.
What Is a Tankless Water Heater?
Before we talk about problems, let’s quickly explain what a tankless water heater does. Unlike traditional water heaters that keep water hot in a storage tank, tankless water heaters heat water only when you turn on a faucet. Water flows through a heating unit, gets heated up instantly, and comes out your tap hot. No waiting for a tank to refill.
Tankless water heaters last longer than traditional ones, usually about 20 years or more. They also save energy because they don’t keep water hot all day long. But they do need regular maintenance and can run into specific issues that are different from traditional water heater problems.
The 5 Most Common Tankless Water Heater Problems
Let’s look at the most common tankless water heater problems you might face and what causes them.
1. Mineral Buildup and Scaling
This is the number one cause of tankless water heater problems. If you have hard water in your area, minerals like calcium and magnesium build up inside your heater. This buildup is called scale. Over time, scale covers the heating elements and clogs the pipes inside your tankless water heater.
When scale builds up, your water heater has to work harder to heat water. This means higher energy bills and slower hot water delivery. Eventually, the buildup can get so bad that your heater stops working completely. You might notice your water takes longer to heat up or doesn’t get as hot as it used to.
The solution? Flush your tankless water heater at least once a year. You can buy a descaling kit and do it yourself, or hire a professional. The process involves running a special cleaning solution through your system to dissolve the mineral buildup. If you have very hard water, you might need to flush your system more often. Installing a water treatment system can also help prevent this problem.
2. System Overload
Tankless water heaters have limits on how much hot water they can produce at once. This is measured in gallons per minute (GPM). If you try to use too much hot water at the same time, your system can’t keep up. This is one of the most frustrating tankless water heater problems for families.
For example, imagine someone is taking a shower while the dishwasher is running and someone else is washing their hands. Your tankless water heater might not be able to heat enough water for all three uses at once. When this happens, the water temperature drops. You might experience lukewarm or even cold water until you reduce the demand.
The solution depends on your situation. If you have a small tankless water heater and a big family, you might need to upgrade to a larger unit with higher GPM. Another option is installing a second tankless water heater to handle the extra demand. You can also avoid using multiple hot water sources at the same time. Professional plumbers can calculate your home’s hot water needs and recommend the right size system.
3. Ignition Failure
Ignition failure is one of the more serious tankless water heater problems. Your heater needs to ignite properly to heat water. Gas tankless water heaters use a flame, while electric ones use heating elements. When ignition fails, you get no hot water at all.
Several things can cause ignition problems. For gas heaters, the most common issues are problems with the gas supply, a dirty igniter, or a faulty flame sensor. Maybe the gas valve isn’t opening properly. Or perhaps there’s not enough ventilation for the system to work safely. Electric tankless water heaters can have problems with their heating elements or electrical connections.
Some ignition failures show error codes on your heater’s display panel. Check your owner’s manual to see what the code means. Simple problems like resetting the system or checking that the gas valve is open might fix the issue. But most ignition failures need professional help. A licensed plumber can diagnose the exact problem and repair your system safely.
4. Cold Water Sandwich Effect
This is a weird problem that’s unique to tankless water heater systems. Here’s what happens: you turn on hot water and it comes out hot at first. Then it suddenly turns cold for a few seconds. Then it gets hot again. This cold burst in the middle is called the cold water sandwich effect.
Why does this happen? When you turn off hot water and then turn it back on quickly, there’s cold water left in the pipes from when the heater shut off. That cold water flows out before the heater can start heating water again. It’s like a sandwich with cold water in the middle of two hot water sections.
This problem is annoying but not dangerous. Some newer tankless water heaters have a small buffer tank that keeps a bit of hot water ready. This reduces the cold water sandwich effect. Another solution is to install a recirculation system that keeps hot water moving through your pipes. You can also just wait a few extra seconds for the water to heat up before stepping into the shower.
5. Venting Issues
Gas tankless water heaters need proper ventilation to work safely. They produce exhaust gases that must go outside your home. If the venting system has problems, your heater might shut down automatically to prevent dangerous gases from staying in your house. This is one of the tankless water heater problems that you should never ignore.
Venting problems can happen for several reasons. The vent pipe might be blocked by debris, birds’ nests, or ice in cold weather. The vent might be too long or have too many bends, which makes it hard for exhaust to escape properly. Or the vent might have been installed incorrectly in the first place.
Signs of venting problems include your heater shutting off unexpectedly, error codes about ventilation, or strange smells. Never try to fix venting issues yourself. These problems involve dangerous gases and require a professional plumber. They’ll inspect your entire venting system, clear any blockages, and make sure everything meets safety codes.
How to Prevent Tankless Water Heater Problems
The best way to handle tankless water heater problems is to prevent them from happening. Regular maintenance keeps your system running smoothly and extends its life. Here’s what you should do.
Schedule annual maintenance with a professional plumber. They’ll flush your system to remove mineral buildup, check all connections, test the ignition system, and inspect the venting. This yearly checkup catches small problems before they become big, expensive repairs. Water heater maintenance is especially important in San Diego’s climate.
Change or clean your water filter regularly if your system has one. A clogged filter can reduce water flow and cause problems. Check your owner’s manual to see how often your filter needs attention.
Keep the area around your tankless water heater clear. Don’t store things right next to it. Make sure there’s good airflow around the unit. This helps it work efficiently and makes it easier for you or your plumber to access it for maintenance.
Pay attention to warning signs. If your water isn’t as hot as usual, if you see error codes, or if you hear strange noises from your heater, don’t wait. Call a professional right away. Small problems are much cheaper and easier to fix than major breakdowns.
Consider a water softener system if you have hard water. This reduces mineral buildup and extends your tankless water heater’s life. It also helps all your other plumbing fixtures and appliances.
When to Call a Professional for Tankless Water Heater Problems
Some tankless water heater problems are easy to fix yourself. Resetting your system or adjusting the temperature settings doesn’t require professional help. But many issues need an expert’s knowledge and tools.
Call a professional plumber if you have no hot water at all. This could be an ignition problem, a gas supply issue, or an electrical problem. These aren’t safe to diagnose or fix on your own.
If you see error codes on your display panel, a plumber can tell you exactly what’s wrong. While some codes might mean simple fixes, others indicate serious problems that need immediate attention.
Water leaks around your tankless water heater need professional help. Even small leaks can cause water damage to your home. A plumber will find where the leak is coming from and fix it properly.
Strange noises like banging, whistling, or rumbling sounds mean something’s wrong inside your system. These sounds might indicate mineral buildup, pressure problems, or failing components. Don’t ignore unusual noises.
If your tankless water heater is more than 15 years old and having frequent problems, it might be time for a replacement. A plumber can evaluate whether repair or replacement makes more financial sense. They’ll help you choose a new system that’s the right size for your home’s needs.
Annual maintenance should always be done by a professional. Even if your system seems to be working fine, yearly service prevents problems and keeps your warranty valid. Many manufacturers require professional maintenance to keep their warranties active.
When you need emergency plumbing help, don’t wait. Solid Plumbing & Drains offers 24/7 service for urgent situations. Whether it’s a complete loss of hot water or a dangerous gas leak, their team responds quickly to protect your home and family.
Keep Your Tankless Water Heater Running Strong
Tankless water heater problems can be frustrating, but most are preventable with regular maintenance. Understanding these five common issues helps you spot warning signs early. Whether it’s mineral buildup, system overload, ignition failure, the cold water sandwich effect, or venting problems, there’s always a solution.
Remember to schedule annual maintenance, watch for warning signs, and call a professional when you need help. Don’t try to fix complex tankless water heater problems yourself. Gas lines, electrical systems, and venting all require expert knowledge to handle safely.
The team at Solid Plumbing & Drains has years of experience with all types of tankless water heater problems. They provide honest, transparent service throughout San Diego County. Their licensed technicians can handle everything from routine maintenance to major repairs. They’ll also help you understand your system better so you can keep it running efficiently.
Protect your investment in your tankless water heater with proper care. Join The Solid Care Plan for just $144 per year to get regular maintenance and catch problems before they start. Or if you’re dealing with tankless water heater problems right now, contact Solid Plumbing & Drains at 858-331-1258. Their expert team will diagnose your issue quickly and get your hot water flowing again. Don’t let tankless water heater problems disrupt your daily routine. Call today for reliable, professional service you can trust.
