Weekly Deals
Water Heaters
Accessories
Installation
Parts
Protection Plans
Why Is My Tankless Water Heater Struggling in Winter? 10 Common Causes and Solutions
When winter arrives in Canada, your tankless water heater may have to work harder than it does during the warmer months. If you notice that your water is not getting hot enough, the temperature fluctuates, the heater does not activate consistently, or your hot water seems to disappear during periods of high demand, colder weather may be contributing to the problem.
A tankless water heater not working in winter can be caused by several different factors. Some issues are related to colder incoming water, while others can involve water flow, mineral buildup, plumbing, ventilation, electrical power, gas supply, or the way the water heater is sized and configured.
Understanding the cause is important because increasing the temperature setting is not always the right solution. In some situations, a simple maintenance step may restore normal performance, while other situations require professional inspection.
This guide covers ten common tankless water heater cold weather problems, explains why they happen, and provides practical solutions for Canadian homeowners.
Colder Incoming Water
One of the biggest reasons a tankless water heater may struggle during winter is the temperature of the water entering the heater.
Unlike a storage water heater that continuously keeps a tank of water heated, a tankless water heater heats water as it passes through the heat exchanger. The colder the incoming water, the greater the temperature increase required to reach your selected outlet temperature.
For example, water entering the home during summer may be considerably warmer than water entering the home during the middle of a Canadian winter. When the incoming water temperature drops, the heater has to provide more heating power to achieve the same outlet temperature.
This can become especially noticeable when several fixtures are being used at the same time.
The solution is to make sure the water heater is appropriately sized for the household's winter conditions and expected hot-water demand. Homeowners should also avoid assuming that simply increasing the temperature setting will solve the problem. A higher setting can increase the required temperature rise and may not address an underlying flow, sizing, or maintenance issue.
If your home consistently experiences low hot-water temperatures during winter, reviewing the heater's capacity, incoming-water temperature, and expected flow rate can help determine whether the system is appropriately matched to your needs.
Insufficient Water Flow
Another possible cause of a tankless water heater low temperature problem is insufficient water flow.
Tankless water heaters generally require a minimum flow rate to activate and continue heating. If the flow through the heater becomes too low, the heater may not activate properly or may have difficulty maintaining the desired temperature depending on the model.
Low flow can happen for several reasons. A partially closed valve, clogged inlet filter, mineral buildup, restrictions in the plumbing, or a low-flow fixture can all affect the amount of water moving through the system.
Winter can make the problem more noticeable because homeowners often use hot water differently during colder weather. A shower, faucet, washing machine, or other fixture may require more hot water than a particular system can comfortably provide under certain conditions.
If you experience inconsistent hot water, check whether the issue occurs at one fixture or throughout the home. If only one fixture is affected, the problem may be related to that fixture or its plumbing rather than the water heater itself.
If multiple fixtures are affected, checking the heater's inlet filter, water flow, valves, and plumbing restrictions may be appropriate.
Mineral Buildup Inside the Water Heater
Mineral buildup is another common reason a tankless water heater may experience reduced performance.
Water naturally contains dissolved minerals, and those minerals can accumulate over time inside plumbing components and the heat exchanger. This process is commonly referred to as scaling.
As scale accumulates, it can interfere with water flow and reduce the efficiency of heat transfer. The result may be longer heating times, temperature fluctuations, reduced performance, or other operating issues.
Hard-water conditions can make mineral buildup more likely, which is why regular maintenance is particularly important for homeowners in areas with harder water.
Descaling is an important part of maintaining a tankless water heater. Following the manufacturer's recommended maintenance procedure and using an appropriate descaling solution can help remove mineral deposits before they become a significant restriction.
If your heater has not been maintained for an extended period and you are experiencing winter performance problems, mineral buildup should be considered as one possible cause.
Always follow the manufacturer's maintenance instructions for your specific model and disconnect the appropriate utilities before performing maintenance.
Frozen or Partially Frozen Plumbing
Freezing temperatures create a particularly important concern for Canadian homeowners because water expands when it freezes.
A tankless water heater itself may not be the only component at risk. Water remaining in exposed pipes, supply lines, valves, or other plumbing components can freeze when temperatures fall below freezing.
This is particularly important for installations in garages, cottages, outdoor areas, utility spaces, or other locations that may experience very low temperatures.
A partially frozen pipe can restrict water flow even before the plumbing freezes completely. If water cannot move properly through the system, the heater may not operate normally.
If you suspect that plumbing has frozen, do not attempt to rapidly heat a frozen pipe with an open flame or another unsafe heat source. Instead, shut off the water supply when appropriate and follow safe thawing procedures or contact a qualified professional.
Preventing freezing is much easier than repairing frozen plumbing. Proper insulation, appropriate installation, maintaining suitable ambient conditions, and following the manufacturer's winterization instructions can help reduce the risk.
For seasonal properties that will be unoccupied during freezing weather, proper winterization is especially important.
Blocked Venting
For gas-powered tankless water heaters, proper venting is essential for safe operation.
During winter, snow, ice, leaves, and other outdoor debris can potentially obstruct vent terminations. Heavy snowfall can cover or partially block an exterior vent, while ice can accumulate around the termination during periods of freezing weather.
A blocked vent can interfere with the heater's operation and may cause safety-related shutdowns.
If your gas tankless water heater suddenly stops operating after heavy snowfall or freezing conditions, inspect the exterior vent termination from a safe location if possible. Look for obvious snow, ice, leaves, or debris blocking the opening.
Do not modify, remove, or improperly alter the venting system. If a blockage cannot be safely cleared or if you suspect a venting problem, contact a qualified technician.
Homeowners should also make exterior vent inspection part of their winter home-maintenance routine, particularly after major snowstorms.
The Water Heater May Be Undersized
Sometimes the heater is working correctly, but the demand placed on it exceeds its available capacity.
Tankless water heaters are typically selected based on factors such as household demand, desired water temperature, incoming-water temperature, and required flow rate.
Winter can expose a sizing problem because colder incoming water requires a greater temperature rise.
For example, a heater that provides satisfactory performance under warmer incoming-water conditions may have more difficulty meeting the same demand when the incoming water becomes significantly colder.
This does not necessarily mean the heater has failed.
If your hot water becomes inadequate primarily when multiple showers, faucets, or appliances operate simultaneously, sizing and demand should be evaluated.
Homeowners considering a new tankless water heater should look at both flow requirements and winter incoming-water temperatures instead of selecting a heater based solely on the maximum flow number shown on the product specifications.
An appropriately sized system can provide more consistent performance throughout the year.
A Dirty Inlet Filter Is Restricting Flow
Many tankless water heaters have an inlet water filter designed to help prevent sediment and debris from entering the system.
Over time, sediment can accumulate on the filter and restrict water flow.
A restricted inlet filter can contribute to low flow and may prevent the heater from operating as expected.
If your tankless water heater has gradually developed inconsistent performance, checking the inlet filter should be part of the troubleshooting process.
Before cleaning the filter, follow the manufacturer's instructions for shutting down the heater and isolating the water supply. Removing or cleaning components without following the correct procedure can result in leaks or equipment damage.
Regular inspection of the inlet filter can be a simple but important part of tankless water heater maintenance.
If the filter repeatedly becomes clogged, there may be sediment or water-quality issues that need further attention.
A Power Interruption Has Affected Operation
Electricity is important even for many gas tankless water heaters because electronic ignition, controls, sensors, and certain protective features require electrical power.
This becomes particularly important during winter.
Some tankless water heaters include freeze-protection features that depend on electrical power. If the power goes out during freezing conditions, those features may not be able to operate.
As a result, a prolonged outage during extremely cold weather can increase the risk of freezing, particularly when the heater is installed in a location exposed to low temperatures.
If your tankless water heater stops working after a power outage, verify that power has been restored and check the appropriate electrical connection or circuit according to the manufacturer's instructions.
If the heater does not restart after power is restored, consult the owner's manual for the applicable reset or troubleshooting procedure.
For homes that experience frequent winter power interruptions, homeowners should also consider how an outage could affect plumbing and freeze protection throughout the property.
Gas Supply Problems
For propane and natural-gas tankless water heaters, an inadequate gas supply can affect performance.
During winter, increased household demand for heating and other gas appliances may place additional demand on the home's gas supply.
Propane systems can also be affected if the fuel supply becomes low. The correct operation of a gas tankless water heater depends on receiving the required fuel supply and pressure specified for the particular model.
If your water heater is producing less hot water than expected, shutting down unexpectedly, or showing an error associated with ignition or combustion, the gas supply should be considered as one possible cause.
Homeowners should not attempt to modify gas pressure or make unauthorized adjustments to gas components.
If you suspect a gas supply issue, contact a qualified professional or the appropriate gas supplier for inspection.
If you smell gas, leave the area and follow your local gas utility's emergency procedures rather than attempting to troubleshoot the water heater yourself.
The Temperature Setting May Not Be the Real Problem
When a tankless water heater is not heating water properly, one of the first things homeowners may consider is increasing the temperature setting.
However, turning the temperature higher is not necessarily the best solution.
A higher temperature setting means the heater must raise the incoming water temperature by a greater amount. During winter, when incoming water is already colder, the required temperature rise can be significant.
If the actual problem is restricted water flow, mineral buildup, a dirty filter, inadequate sizing, frozen plumbing, or a gas or electrical issue, increasing the temperature setting will not fix the underlying problem.
Instead, homeowners should first determine what is causing the reduced performance.
Check the water flow, inspect for obvious plumbing restrictions, review maintenance requirements, and confirm that the heater is receiving the required power or gas supply. For gas models, exterior venting should also be checked for visible snow or debris.
The appropriate temperature setting will depend on the household's needs, the installation, and the manufacturer's recommendations.
Why Winter Can Make Existing Problems More Noticeable
One important thing to remember is that winter does not always create the original problem.
Instead, colder weather can make an existing issue more noticeable.
A partially restricted inlet filter may not cause obvious problems when incoming water is relatively warm. A heater that is marginally sized for the household may appear adequate during periods of lower demand. Minor mineral buildup may not be noticeable until the incoming water temperature drops.
Once winter arrives, the combination of colder water and higher demand can expose those limitations.
This is why preventative maintenance before winter can be so valuable.
Cleaning filters, performing recommended descaling, checking plumbing, inspecting gas vent terminations, confirming proper operation, and preparing vulnerable plumbing for freezing temperatures can help homeowners identify potential problems before the coldest part of the season arrives.
What to Do If Your Tankless Water Heater Is Not Heating Water
If your tankless water heater is not heating water during winter, start with simple observations rather than immediately changing the temperature setting.
First, determine whether the problem affects one fixture or the entire home.
Next, check whether the heater is receiving power and whether the appropriate circuit or electrical connection is functioning.
For gas models, verify that the fuel supply is available and that the exterior vent termination is not visibly blocked by snow, ice, or debris.
Check the manufacturer's recommended maintenance schedule and determine whether the inlet filter requires cleaning or whether the system is due for descaling.
You should also consider whether the problem occurs only when several fixtures are operating simultaneously. If so, household demand and heater sizing may need to be evaluated.
If you suspect frozen plumbing, do not use unsafe heating methods to thaw pipes. A qualified plumber or technician can help determine whether the plumbing or water heater has been affected.
Finally, pay attention to any error codes displayed by the water heater. Your owner's manual can provide information about what a particular code means and what steps should be taken.
How to Prevent Tankless Water Heater Winter Problems
Preventing tankless water heater freezing and other winter problems begins before temperatures reach their lowest point.
Fall is an ideal time to inspect the installation and complete recommended maintenance.
Homeowners should make sure exposed plumbing is properly protected against freezing temperatures. Outdoor vent terminations for gas models should remain clear of snow, ice, leaves, and other obstructions. The water heater's inlet filter should be checked according to the manufacturer's maintenance recommendations, and descaling should be performed when necessary.
It is also important to understand your home's hot-water demand and make sure the water heater is appropriately sized for the installation.
For seasonal homes, cottages, garages, or other locations that may be left unoccupied during winter, follow the manufacturer's winterization instructions carefully.
Planning ahead can help reduce the possibility of discovering a water-heating problem when temperatures are already well below freezing.
When to Contact a Professional
Some tankless water heater problems can be addressed through routine homeowner maintenance, but other situations require professional assistance.
Contact a qualified professional if you suspect a gas supply problem, combustion issue, venting problem, frozen plumbing, electrical fault, or internal equipment failure.
You should also seek professional assistance if the water heater continues to shut down, produces persistent error codes, leaks water, or fails to provide adequate hot water after basic troubleshooting and recommended maintenance.
Gas and electrical components should only be serviced by appropriately qualified professionals.
When troubleshooting your water heater, always follow the manufacturer's instructions and safety warnings for your specific model.
Final Thoughts
A tankless water heater not working in winter does not necessarily mean that the water heater has failed. Canadian winter conditions can place additional demands on a tankless system because incoming water temperatures can drop significantly, increasing the amount of heating required to reach the desired outlet temperature.
Cold weather can also make problems involving water flow, mineral buildup, filters, frozen plumbing, venting, sizing, electrical power, gas supply, and temperature settings more noticeable.
The key is to identify the underlying cause rather than simply increasing the temperature setting.
With regular maintenance, proper sizing, protected plumbing, clear venting, adequate water and gas flow, and appropriate winter preparation, homeowners can help their tankless water heater perform reliably through the colder months.
For Eccotemp homeowners, following the maintenance and operating instructions specific to your model is the best starting point whenever winter performance changes. If a problem persists or involves gas, electrical, combustion, or frozen plumbing components, professional service can help determine the cause and get the system operating safely again.
Frequently Asked Questions
Why does my tankless water heater struggle in winter?
A tankless water heater can struggle during winter because colder incoming water requires a greater temperature rise to reach the desired outlet temperature. Other factors, such as restricted water flow, mineral buildup, inadequate sizing, frozen plumbing, power interruptions, or gas supply problems, can also contribute to reduced performance.
Why is my tankless water heater producing cold water in winter?
Cold water during winter can be caused by several factors, including very cold incoming water, insufficient flow, mineral buildup, a dirty inlet filter, inadequate system capacity, or a problem with the gas or electrical supply. Checking the specific symptoms and any displayed error codes can help identify the cause.
Can a tankless water heater freeze in winter?
Yes. Tankless water heaters and connected plumbing can be vulnerable to freezing temperatures, particularly when installed in cold locations or when power is interrupted. Proper installation, freeze protection, plumbing insulation, and winterization can help reduce the risk.
Does increasing the temperature fix a tankless water heater that is not heating properly?
Not necessarily. Increasing the temperature setting may not solve problems caused by restricted flow, mineral buildup, frozen plumbing, inadequate sizing, electrical interruptions, or gas supply issues. The underlying cause should be identified first.
How can I prevent tankless water heater problems during Canadian winter?
Regular maintenance before winter can help. Homeowners should check the inlet filter, perform recommended descaling, protect exposed plumbing from freezing, keep gas vent terminations clear of snow and debris, confirm adequate power or gas supply, and make sure the water heater is appropriately sized for household demand and winter conditions.
