What it isTankless water heaters heat water as it flows through a heat exchanger instead of storing it. Their problems look different from tank heaters: error codes, ignition failures, flow that is too low to activate the burner, scale buildup in the heat exchanger, and venting or condensate issues on condensing models.
When you need tankless water heater repair
- An error code on the controller
- Hot water that cuts out during use
- Brief cold-water bursts between hot (often a normal "cold water sandwich", but worse than usual)
- Lower hot water flow than before
- Unit fails to ignite
How it works
- Read the error code and check the manufacturer's code table.
- Clean the inlet filter screen.
- Descale the heat exchanger with a pump and approved descaling solution through the service valves.
- Check gas supply sizing, ignition, flame sensor and venting.
- On condensing units, check the condensate drain and neutralizer.
Limits and when it’s not the right fix
- Undersized gas lines cause chronic problems that parts cannot fix.
- Very low flow fixtures may not reach a unit's minimum activation flow.
- Some repairs require manufacturer-specific parts or certified service.
What affects the cost
We don’t publish national price figures because real quotes vary too much by region, access and the condition of your system. These are the factors that move the price:
- Error and component involved
- Descaling needed
- Gas supply or venting corrections
- Parts availability
Ask for a written quote that names the method, materials and any permit or restoration work before work begins.
Tankless Water Heater Repair: common questions
How often should a tankless water heater be descaled?
Many manufacturers suggest yearly descaling, and more often with hard water. Check the manual for your model.
Why does my tankless water heater go cold in the middle of a shower?
Flow dropping below the activation threshold, scale in the heat exchanger, gas supply problems, or a clogged inlet filter are common reasons.
What is a cold water sandwich?
A short burst of cold water between hot water, felt when a tap is turned off and back on quickly. Some is normal for tankless units; recirculation or a small buffer tank can reduce it.
