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uk Home & property emergencies

What to do if…
you suddenly have no hot water and your water heater shows an error or warning light

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

Short answer

First check for danger signs: if you smell gas, a carbon monoxide alarm sounds, or someone has sudden symptoms near the appliance, get everyone into fresh air and call the correct gas emergency number for where you are. If there are no danger signs, take a photo of the error or warning light and contact your landlord, managing agent, or a Gas Safe registered engineer.

Do not do these things

  • Do not keep resetting the boiler or water heater if it locks out or shows the warning again.
  • Do not remove covers, open a sealed case, or try internal repairs.
  • Do not ignore a carbon monoxide alarm, gas smell, soot marks, scorch marks, or sudden symptoms such as headache, dizziness, nausea, confusion, chest pain, or breathlessness.
  • If you may have a gas leak, do not smoke, use naked flames, or turn electrical switches on or off.
  • Do not let anyone who is not Gas Safe registered work on a gas appliance.
  • Do not use hot taps, showers, or the appliance again if you have been told it is unsafe.

What to do now

  1. Check for immediate danger signs.

    • If you smell gas, open doors and windows if you can do this safely, get everyone into fresh air, and call the gas emergency number from outside or away from the smell.
    • In England, Scotland, or Wales, call 0800 111 999 for a natural gas emergency.
    • In Northern Ireland, call 0800 002 001 for a natural gas emergency.
    • If someone is seriously unwell, has collapsed, is confused, has chest pain, or is struggling to breathe, call 999.

  2. If a carbon monoxide alarm sounds, treat it as urgent.

    • Stop using the appliance if you can do this safely.
    • Open doors and windows if you can.
    • Move everyone outside or into fresh air.
    • Do not go back in until you have had safety advice.

  3. Make the area safe without touching the inside of the appliance.

    • Stop using hot taps and showers for now.
    • Keep people away from the boiler, water heater, cylinder, or airing cupboard.
    • If there is water near electrical parts, do not touch the appliance or nearby switches; keep people away and call for urgent help if there is immediate danger.

  4. Record the fault information.

    • Take a clear photo of the fault code, flashing lights, warning screen, pressure gauge if visible, and make or model label.
    • Note what happened just before the fault, such as a power cut, timer change, very cold weather, loss of pressure, recent work, or a leak.

  5. Do only simple external checks.

    • Check whether the electricity has tripped at the consumer unit, but only if there is no gas smell, no carbon monoxide concern, and no water near electrics.
    • Check whether the appliance display is on.
    • If you have a combi boiler, note the pressure-gauge reading if you can see it without opening anything.
    • Do not top up pressure, change valves, or alter settings unless the manufacturer’s user instructions clearly tell you to and you feel sure it is safe.

  6. Contact the right person and send the photos.

    • If you rent, report “no hot water plus warning light or fault code” to your landlord, agent, housing association, or repairs line.
    • If you own the home and the appliance uses gas, contact a Gas Safe registered engineer.
    • If it is electric-only, such as an immersion heater, contact a qualified electrician, heating engineer, or plumber as appropriate.
    • Say whether there are any safety signs, water leaks, vulnerable people, or no other way to wash.

  7. Only try one reset if it is clearly safe.

    • Only do this if there is no gas smell, no carbon monoxide alarm, no concerning symptoms, no water near electrics, and the manufacturer’s user controls clearly explain how to reset it.
    • If the error or warning comes back, stop and wait for professional help.

What can wait

  • You do not need to diagnose the fault code now.
  • You do not need to buy parts, remove panels, bleed anything, or decide whether to repair or replace the appliance.
  • You do not need to optimise timers, schedules, smart controls, or temperature settings until the system is safe and working again.
  • If you rent, legal escalation can wait until you have reported the fault clearly and kept a record of the report.

Important reassurance

A warning light or lockout often means the appliance has stopped itself rather than continuing in an unsafe or damaging state. The useful first steps are to rule out gas and carbon monoxide danger, capture the fault information, and get the right person involved.

Scope note

These are first steps only. Later decisions about repair, replacement, landlord duties, complaints, or electrical and gas safety may need help from a qualified engineer, your landlord or agent, a housing adviser, or emergency services.

Important note

This is general safety and first-response information, not legal, medical, engineering, electrical, gas-safety, or professional advice. If you suspect gas, carbon monoxide, fire, electric shock risk, or serious illness, prioritise fresh air and urgent help.

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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