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uk Home & property emergencies water heater leaking • hot water cylinder leaking • boiler cupboard leak • immersion heater leak • hot water tank leak • water heater popping noises • hot water cylinder banging • rumbling water heater • noisy hot water tank • dripping from pressure relief pipe • overflow from tundish • leak near airing cupboard • sudden hot water leak • water near electrics • gas water heater concern • carbon monoxide worry • stopcock shut off • isolate cold feed valve • shut off immersion power • landlord hot water emergency

What to do if…
your water heater starts leaking or making unusual popping noises

Short answer

Turn off the heater’s power (and gas supply if it’s gas-fired), then stop the water feed to the heater to limit damage. If you smell gas, suspect carbon monoxide, or hear loud/violent noises, get everyone into fresh air and call the gas emergency number.

Do not do these things

  • Do not ignore a new leak or repeated loud popping/banging—treat it as urgent even if you still have hot water.
  • Do not touch a wet switch, plug, or fused spur, and do not stand in water while handling electrics (shock risk).
  • Do not try to dismantle or “tighten” valves/pipework on a pressurised (unvented) hot water cylinder.
  • Do not block, cap, or tape over a discharge/overflow pipe (including a tundish discharge).
  • Do not light matches, use naked flames, or create sparks if you smell gas.
  • Do not keep using hot water if you suspect overheating (very hot water, banging, relief/discharge running).

What to do now

  1. Do a 10-second danger check.
    • If you smell gas, a CO alarm sounds, or people feel suddenly unwell in a way that could be carbon monoxide (headache/dizziness/nausea): open doors/windows as you leave, get everyone into fresh air, and call the National Gas Emergency Service (0800 111 999).
  2. Turn off heat to the water heater (without touching wet electrics).
    • Immersion heater / hot water cylinder: switch off at the fused spur/isolator (often near the cylinder).
    • If that area is wet or you’re unsure, turn off the relevant circuit at the consumer unit (only if you can do so from a dry, safe position).
    • Gas-fired water heater/boiler providing hot water: turn the appliance controls to OFF only if it’s safe to access. If there’s any gas smell, prioritise Step 1.
  3. Stop the water feeding the heater (to slow/stop the leak).
    • Turn off the cold-water inlet/isolating valve on the pipe feeding the cylinder/heater.
    • If you can’t find it (or the leak is fast), turn off the home’s water at the stopcock/stop tap.
  4. Reduce damage safely.
    • Put a bucket/tray under drips and use towels to guide water away from electrics and ceilings.
    • Move nearby items (especially anything electrical) out of the wet area.
  5. If water is discharging via a tundish/discharge pipe or the noises are loud: treat it as urgent.
    • For an unvented hot water cylinder, visible discharge (often via a tundish) can indicate a pressure/temperature safety device operating. Keep the system off and contact an engineer competent to work on unvented cylinders (often described as G3/unvented qualified).
  6. Call the right help for your situation.
    • If you rent: contact your landlord/agent’s emergency repairs line and say you’ve isolated power/heat and water.
    • If you own: call a qualified plumber/heating engineer. If it’s gas-fired, use a Gas Safe registered engineer.
  7. Document quickly (for repairs/insurance), then step back.
    • Take photos/videos of the leak source area, any discharge/tundish flow, and any water damage—then leave the unit off until inspected.

What can wait

  • You do not need to diagnose the cause (scale/sediment, valve fault, corrosion) right now.
  • You do not need to drain the whole cylinder/tank unless a professional tells you to.
  • You do not need to decide about replacement today—first stabilise (off + isolated + contained), then get it assessed.

Important reassurance

Water heater leaks and sudden noises are common panic triggers because they combine heat, pressure, water, and sometimes gas/electricity. Turning off the heat source and isolating the water supply is usually enough to stabilise things until a professional can take over.

Scope note

This is first steps only—aimed at making the situation safer and preventing damage. A qualified professional may need to test safety devices and repair or replace parts.

Important note

This is general information, not a diagnosis. If you suspect gas leakage or carbon monoxide, prioritise getting everyone into fresh air and using the official gas emergency route.

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