Tankless Water Heater Repair
Most tankless problems come from scale in the heat exchanger, an ignition fault or a dirty flow sensor. Write down the error code; it tells the plumber where to start.
Symptoms, causes and costs
| Situation | Usual cause | Typical cost |
|---|---|---|
| Error code, no hot water | Ignition failure, flame rod, gas supply | $150 to $450 |
| Hot then cold bursts | Low flow, scale, mixing issue | $150 to $400 |
| Lukewarm water only | Scale in heat exchanger, undersized unit | $150 to $350 descale |
| Unit won't power on | Power supply, PCB board, fuse | $200 to $600 |
National ranges from published cost guides. Your plumber quotes your job after seeing the heater.
Tankless Water Heater Repair, explained
Scale is the big one
Hard water leaves mineral scale inside the heat exchanger. The unit overheats, throws codes and delivers uneven temperatures. Descaling with a pump and vinegar or descaling solution clears it, and most makers recommend it yearly on hard water.
Ignition and flame faults
If the unit clicks but won't light, or lights and shuts off, the cause is often gas pressure, a dirty flame rod or an ignition issue. Winter venting problems from snow or ice also cause these faults.
When to replace a tankless unit
Tankless heaters often last 20 years. A failed heat exchanger on an older unit can cost close to a new one, so that's when replacement comes up.
Do this first
- Write down the error code exactly as it shows.
- Check the gas valve is fully open and the vent outside isn't blocked by snow or debris.
- Clean the inlet filter if your model has one.
- Don't reset it over and over. Some units lock out after repeated faults.
Related water heater services
Tankless Water Heater Repair questions
How often should a tankless water heater be descaled?
Once a year on hard water is a common recommendation. Soft-water homes can go longer.
Why does my tankless heater give a cold water sandwich?
When you turn the tap off and on, there's a short gap while the burner relights. It's normal for many units, but a long or new cold burst points to a problem.
Can any plumber fix a tankless heater?
Tankless units need some brand-specific knowledge. Mention the brand and model when you call.
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