You go to take a shower, and the water never heats up. Or you check the unit, and the pilot light is out. Either way, a water heater that won't ignite leaves you without hot water, and it’s one of the more stressful plumbing problems to handle because the cause is not always obvious.
The troubleshooting process varies depending on whether you have a traditional tank water heater or a tankless unit, since their ignition systems operate differently. This guide covers the most common reasons each type might fail to ignite, along with a few things you can check yourself before calling a plumber.
No hot water in Plano, TX? Call DNA Plumbing Heating and Air at (214) 817-3755 or contact us online, and our team can diagnose the issue with upfront pricing and no guesswork.
Tank Water Heater: Why It Won't Ignite
Gas tank water heaters use either a pilot light system or electronic ignition to ignite the burner. Below, we discuss the most common causes of ignition failure.
1. The Pilot Light Is Out
On older units with a standing pilot, the pilot flame burns continuously. If it goes out due to a draft or a temporary gas supply interruption, the main burner loses its ignition source. Most units have a relighting procedure printed on the label, and the solution is often as simple as following those steps.
2. A Failed Thermocouple
The thermocouple is a safety sensor placed in the pilot flame. It detects if the flame is lit and signals the gas valve to stay open. When the thermocouple fails or becomes coated with oxidation, it mistakenly signals that the flame is out, causing the gas valve to shut off even if the flame is still burning. This is one of the most common ignition issues our technicians encounter on tank units, and it is a simple repair.
3. Gas Supply Issues
If the gas valve to the water heater was accidentally turned off or if there's a supply interruption affecting other gas appliances in the home, the burner will not light, no matter what else you try. Ensure the shutoff valve is fully open (handle parallel to the pipe) and verify that other gas appliances, such as your stove, are functioning properly.
4. A Faulty Gas Valve or Control Board
If the thermocouple tests correctly and the gas supply is confirmed, then the gas valve itself might have failed. A faulty valve won't allow gas to reach the burner even if all other parts are working properly. This situation requires replacement by a licensed technician.
Tankless Water Heater: Why It Won't Ignite
Tankless units heat water on demand using an electronic igniter and gas burner. When they fail to ignite, they usually display an error code. Check the error code first, as it often directly indicates the cause.
1. No Error Code and No Hot Water
If the unit turns on but doesn’t produce heat or display an error code, inspect the cold-water inlet for debris or a clogged filter screen. Low water flow stops the flow sensor from activating, preventing ignition from starting.
2. Ignition Failure Error Code
Most tankless units will show an ignition failure code (usually something like Code 11 or Code 10, depending on the brand) when the burner doesn’t light after several tries. This is generally caused by a gas supply problem, a blocked flue vent, or a dirty igniter. Make sure the gas supply valve is open. Then inspect the exhaust vent and air intake for blockages, especially bird nests, debris, or pest activity in the outdoor venting.
3. Venting Problems
Tankless water heaters need an air intake and an exhaust vent to function properly. A blockage in either causes the unit to shut down as a safety precaution. In Plano and the surrounding DFW area, venting problems increase in late winter and early spring when birds and small animals begin nesting in exterior vents.
4. Scale Buildup in the Heat Exchanger
DFW has hard water, and mineral scale builds up inside the heat exchanger. Heavy scale lowers heating efficiency, triggers overheating sensors, and can eventually cause ignition failures. Tankless units in this area benefit from annual descaling to prevent this. Our technicians perform descaling as part of routine water heater maintenance and can tell you whether scale is contributing to your ignition problem.
What You Can Check Before Calling
For tank units: Check whether the pilot light is out, then follow the relighting instructions on the unit label. Make sure the gas valve is open and that other gas appliances are working properly. If the pilot relights but goes out again within 30 seconds, the thermocouple probably needs to be replaced.
For tankless units: Note the displayed error code. Ensure that the gas valve is open. Check the inlet filter screen for debris. Inspect the exterior venting for obvious blockages. If those steps don't resolve the issue, a technician's diagnosis is necessary.
Water heater ignition issues rarely stem from a single part failure. At DNA Plumbing Heating and Air, our team uses a systematic diagnostic process to deliver an accurate diagnosis and repair that targets the root cause. Whether it's a thermocouple on a tank unit or a venting problem on a tankless, we provide upfront pricing before starting any work.
Water heater won't ignite in Plano, TX? Call (214) 817-3755 or schedule online. We serve Plano and the surrounding areas with flexible availability for water heater diagnostics.
