Tankless gone cold? Start here
What to note before calling
Read the display
Many units show a fault code. Write it down or take a photo; do not clear it.
One tap or all?
If only one fixture is cold, the unit may be fine and the issue is at that fixture.
How much flow?
A trickle may not trigger the unit. Notice whether full-flow taps get hot.
Propane supply
On a propane home, check the supply tank has fuel before anything else.
If you smell gas near the unit or anywhere indoors, leave the house and call the gas utility and emergency services from outside.
If the carbon monoxide alarm sounds while the unit is running, leave the house and call emergency services from outside.
Common tankless problems
Scale in the heat exchanger
The most common cause of fading output, fluctuating temperature and fault codes, especially on hard well water. Minerals coat the narrow passages, reduce flow and make the unit overheat or shut down. Descaling usually restores it.
Not enough hot water in winter
If the unit was sized for warm inlet water, it may fall short when the water coming in is at its coldest. Nothing has failed; the unit is at its limit. See tankless installation on sizing.
Ignition and flame faults
Igniters, flame sensors and gas valves can fail, and propane units stop if the supply runs low.
Venting and air intake problems
Blocked intakes or vents, including snow or ice over a side-wall termination in winter, can trigger safety shutdowns. Do not try to clear or adjust venting yourself; mention it when you call.
Flow sensor and inlet filter issues
A clogged inlet screen, often with sediment from a well, or a failing flow sensor can stop the unit recognising that a tap is open.
On a private well?
Well water and tankless units
Scale builds faster on some well water, and grit can clog the inlet screen. If your unit has needed descaling before or keeps showing flow or overheating faults, say so. The technician will descale, clean the inlet screen, and suggest a sensible interval for your water.
Descaling intervals set for your water.
What to leave alone
- Clearing fault codes or cycling the unit's power
- Opening the cover or touching internal wiring
- Gas lines and connections
- Vent pipes and terminations, including snow and ice around them
- Isolation valves and descaling connections
How repair works
The technician reads the fault history, checks fuel supply, ignition and flame sensing, inspects the venting and air intake, checks flow sensing and the inlet screen, and assesses the heat exchanger for scale. They explain the fault and give the price before repairing. Descaling uses the unit's isolation valves and a pump to circulate a descaling solution through the heat exchanger.
Repair or descale, priced first.
Repair or replace?
Most tankless faults are repairable, and descaling restores many units that seemed to be failing. Replacement makes sense when the heat exchanger itself has failed, parts are no longer available for an older unit, or the unit was never large enough for the household. In the last case, a larger unit or a different type of heater may be the better answer.
Winter-specific tankless problems
Connecticut winters bring a cluster of tankless calls. Side-wall vents and air intakes can be covered by snow or glazed with ice, tripping safety shutdowns. Condensate lines on condensing units can freeze where they run through cold spaces or outside. Units installed in unheated spaces can be damaged if water inside them freezes. And the colder inlet water means a unit that was marginal in autumn can no longer keep up. When you call in winter, mention whether there has been heavy snow or a hard freeze; it helps the technician narrow things down before arriving.
Descaling, explained
Descaling means isolating the unit from the household plumbing using its service valves, connecting a small pump, and circulating a descaling solution through the heat exchanger for a period to dissolve mineral build-up. The unit is then flushed with clean water and returned to service. Done at the right interval for your water, it keeps output and flow up and reduces overheating faults. On hard well water, it is the single most useful maintenance step for a tankless unit. If your unit was installed without service valves, the technician can add them to make future descaling simpler.
What fault codes are, and are not
A fault code is the unit's record of what its sensors noticed when it shut down: no flame, overheating, a venting problem, low flow and so on. It points the technician in a direction, but it does not always name the root cause. An overheating code, for example, may come from scale rather than a failed sensor. That is why the technician confirms the cause before replacing parts, and why we ask you not to clear codes before the visit.
Service valves make repairs easier
Tankless units installed with isolation or service valves on the water connections can be descaled and serviced without disturbing the rest of the plumbing. If yours lacks them, the technician may suggest adding them during a repair, which makes every future descale quicker and simpler.
What affects the cost of tankless water heater repair
- Descaling against replacing a component
- Parts availability for the brand and model
- Venting repairs or changes
- Emergency hours versus a scheduled call
How long tankless water heater repair takes in Connecticut
Descaling and common part replacements are usually done in one visit. Brand-specific parts may need ordering. Once running, a tankless unit delivers hot water immediately.
If the unit needs a part that has to be ordered, the technician will tell you whether it can be left running in a limited way in the meantime or whether it needs to stay off until the part arrives.
Tankless repair questions
My tankless heater shows an error code. What does it mean?
Codes vary by brand. Note the code and the brand when you call; it helps the technician prepare. Please do not clear the code, since the history helps with diagnosis.
Why does my tankless unit go hot and cold?
Common causes include scale in the heat exchanger, a flow rate near the unit's minimum, a failing sensor, or several fixtures running at once in winter. A technician can find which.
How often should a tankless unit be descaled?
It depends on the water. Hard well water may need descaling much more often than soft town water. After a first descale, the technician can suggest an interval.
Snow covered the vent outside and the unit stopped. What should I do?
Call a technician. Blocked vents and intakes trigger safety shutdowns, and venting should be checked by a professional rather than cleared and restarted without a look.
Why is there no hot water at a trickle?
Tankless units need a minimum flow to fire. A very low flow at a sink may not trigger it. This is normal behaviour rather than a fault.
Can you repair any brand?
The local installers work on the common brands found in Connecticut homes. Parts for older or less common models can take time. Tell us the brand when you call.
My propane tankless stopped. Is it the propane?
It might be. Check the supply tank has fuel. If it does, the fault is likely ignition, flame sensing or venting, and a technician should look.
Is it worth fixing an older tankless unit?
Often, if the heat exchanger is sound and parts are available. If the heat exchanger has failed or the unit was always too small, replacement may be the better value. The technician will explain.
Why does my tankless unit shut off in the middle of a shower?
Common causes include overheating from scale, a flow sensor issue, or a venting safety shutdown. In winter, a blocked vent or intake is a frequent culprit. The fault code and the circumstances help the technician pin it down.
Can scale damage a tankless unit permanently?
Heavy scale that is left for a long time can contribute to heat exchanger failure. Regular descaling on hard water is the best way to avoid that.