Tankless Water HeaterTroubleshooting2026-01-24
Tankless No Hot Water: Causes
No hot water from a tankless unit can be ignition, gas supply, scale, or an error-code lockout.
A tankless water heater with no hot water usually shows an error code that points to the cause. Here's what to check.
Common causes
Gas-supply issues, ignition failure, a clogged inlet filter, scale build-up reducing flow, or a flow sensor not detecting demand are common reasons for no hot water.
Read the error code
Tankless units display fault codes that identify the issue. Note the code before calling — it speeds diagnosis and repair.
Key takeaways
- Note the error code on the display
- Check gas supply and that other gas appliances work
- Clean the cold-water inlet filter
- Descaling may be needed in hard water
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Frequently asked questions
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