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uk Home & property emergencies

What to do if…
your water heater is leaking, discharging water, or making loud banging noises

Produced and maintained by PanicStation.org Published: Last reviewed: Editorial policy UK guide

Short answer

Stop using the heater and keep away from escaping hot water, steam, wet electrics, or a swollen or distorted cylinder. Switch it off only if its controls are dry and safely accessible, then arrange an urgent inspection by an appropriately qualified heating engineer or plumber.

Do not do these things

  • Do not touch the heater, switches, plugs, sockets, or consumer unit while standing in water.
  • Do not remove covers or attempt to repair internal parts yourself.
  • Do not cap, plug, clamp, or block any discharge, overflow, vent, or pressure-relief pipe.
  • Do not keep reheating the water to test whether the leak or banging stops.
  • Do not approach forcefully escaping water or steam.
  • Do not force a seized water or gas isolation valve.
  • Do not use a gas appliance that you suspect is unsafe.
  • Do not operate electrical switches or use flames inside the property if you smell gas.

What to do now

  1. Move people and pets away from the heater, leaking water, and any discharge outlet. Leave the immediate area if there is steam, forceful spraying, fire, a visibly distorted cylinder, or water reaching electrical equipment.
  2. Turn the heater off using its normal controls if you can do so without entering water or touching anything wet. For an electric heater, isolate its dedicated supply only when the switch or consumer unit is dry and safely accessible. Do not open the appliance casing.
  3. If water is escaping into the property, move possessions out of its path and place a container beneath a slow drip only when this does not bring you close to hot water, steam, or electrics.
  4. If the leak is substantial and you know which water isolation valve or main stop tap controls the supply, close it only if it is accessible and safe to operate. Do not force it.
  5. Leave all discharge, overflow, vent, and pressure-relief pipes unobstructed. Continuous or repeated discharge may indicate a fault requiring professional inspection.
  6. Contact an emergency plumber or heating engineer. Work on a gas appliance must be carried out by a Gas Safe registered engineer. An unvented hot-water cylinder should be assessed by a person competent to work on that type of system.
  7. If you rent, report the fault promptly through your landlord’s, letting agent’s, council’s, or housing association’s repairs service. State whether water is still flowing, whether electrics are affected, and whether you have switched off the heater or water supply.
  8. If you smell gas, get everyone into fresh air, avoid flames and electrical switches, and call the gas emergency service from outside. In England, Scotland, and Wales call 0800 111 999. In Northern Ireland call 0800 002 001.
  9. If a carbon monoxide alarm sounds, or someone may have been exposed to carbon monoxide, move into fresh air and seek medical advice. Call 999 or go to A&E if anyone has difficulty breathing, sudden confusion, loss of consciousness, weakness, or chest or muscle pain.

What can wait

You do not need to identify the failed component, drain the system, choose a replacement heater, settle insurance questions, or decide who must pay right now. First make the area safe, stop using the heater, limit water damage where safe, and arrange professional help.

Important reassurance

A leak, discharge, or banging noise does not by itself show exactly what has failed. Stopping use, keeping clear of hot water and wet electrics, leaving safety outlets open, and arranging a qualified inspection are sensible immediate precautions.

Scope note

This guide covers immediate safety and damage-limitation steps only. Diagnosis, repair, insurance claims, tenancy responsibilities, and replacement decisions may require a qualified tradesperson, your landlord, your insurer, or another relevant specialist.

Important note

This is general safety information, not plumbing, electrical, gas, legal, medical, insurance, or other professional advice. Follow instructions from emergency services, the appliance manufacturer, your landlord or housing provider, and qualified professionals who can assess the property directly.

Additional Resources

Closely connected guides that may be useful during the same situation or its immediate aftermath.

About this guide

This guide was produced and is maintained by PanicStation.org using its published editorial process. Official and specialist sources are checked where relevant, and AI-assisted tools may be used for drafting, organisation, and consistency checks. The site operator remains responsible for publication, revision, and removal decisions.

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