Gas Water Heater Not Heating

Common Symptoms

• No hot water at any tap
• Pilot light is out or won't stay lit
• Status light on gas valve flashing fault code
• Water is lukewarm but not hot
• Popping or rumbling sounds from tank (scale buildup affecting heating)

Most Likely Causes

1. 1

   Pilot Light Out (Most Common)

   The pilot flame has been extinguished by a draft, gas interruption, or thermocouple failure. Without the pilot, the gas valve won't open and the main burner can't fire. Relighting the pilot per the label instructions resolves this instantly if the thermocouple is still good.

2. 2

   Bad Thermocouple

   The thermocouple is a safety device that generates a small millivolt current (20–30mV) when heated by the pilot flame, signaling the gas valve to stay open. A failing thermocouple generates insufficient voltage and causes the gas valve to shut off the pilot. This is the single most common water heater repair.

3. 3

   Failed Gas Valve

   The combination gas valve controls both the pilot and main burner gas flow. When it fails internally — usually a stuck solenoid or failed thermopile — the pilot won't light or stay lit, or the main burner won't fire even with a good thermocouple reading. A faulty gas valve typically costs $80–$150 to replace and is a definitive fix if thermocouple tests good.

4. 4

   Low Gas Pressure

   If other gas appliances in the home also have weak flames or are off, low gas pressure from the utility side or a partially closed shutoff valve is the cause. Check that the gas shutoff valve at the water heater is fully open (handle parallel to pipe), and verify the gas meter service hasn't been interrupted.

Quick DIY Checks

1. 1Relight the pilot following the exact instructions on the water heater label — hold the pilot button down for 30–60 seconds to heat the thermocouple before releasing. If it relights and stays lit, you're done.
2. 2Test thermocouple output with a multimeter set to millivolts DC. With the pilot lit, connect meter leads to the thermocouple's output terminal and ground. A good thermocouple reads 20–30mV; below 15mV means replace it.
3. 3Inspect the gas supply: confirm the shutoff valve at the water heater is fully open (handle parallel to the supply pipe), and check whether other gas appliances in the home are working normally.

Repair vs Replace

Recommended Tools & Parts

• Universal Thermocouple

  24-inch universal fit thermocouple compatible with most gas water heaters. Replaces failed thermocouples that cause pilot outage.

  $12–$20

  Buy on Amazon →

• Gas Valve (OEM)

  Combination gas valve for gas water heaters — controls pilot and main burner gas flow. Match to your heater brand and BTU rating.

  $80–$150

  Buy on Amazon →

• Pilot Assembly Kit

  Complete pilot burner assembly including thermocouple and pilot tube — used when individual thermocouple replacement doesn't resolve the issue.

  $20–$40

  Buy on Amazon →

• Anode Rod

  Magnesium or aluminum anode rod to replace the sacrificial rod and extend tank life. Replace every 3–5 years to prevent tank corrosion.

  $20–$35

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

Related Repair Guides

This section combines editorial `relatedSlugs` from the article source with metadata-based matches so each guide links deeper into the repair library.