Water flows but remains completely cold; Marey gas tankless heater shows normal display with no error code.

Safety first: Turn OFF gas and power before internal inspection. If you smell gas, ventilate and do not ignite flames or operate electrical switches.

Steps:

• Confirm gas supply: Ensure the manual gas shutoff valve to the heater is fully open. Check that other gas appliances work.
• Check demand: Open a hot tap fully to ensure sufficient flow to trigger ignition.
• Inspect burner area: Remove the cover and look for obvious debris or soot around the burner and igniter. Clean gently.
• Observe ignition sequence: With the cover on or using the viewing window, restore gas and power, then open a hot tap. Listen for clicking (igniter) and gas flow. If there is no clicking or flame, the igniter or gas valve may be faulty.

When to call a technician: For gas valve testing, ignition system diagnosis, or if you are not comfortable working with gas.