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uk Home & property emergencies

What to do if…
your boiler pressure drops suddenly and the heating or hot water stops working

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

Short answer

If you smell gas, suspect carbon monoxide, or a carbon monoxide alarm is sounding, get everyone into fresh air and call the correct gas emergency number for where you are. If there is no gas or carbon monoxide concern, check the pressure gauge and make one careful top-up only if you can clearly identify the filling control and your boiler instructions support it.

Do not do these things

  • Don’t stay inside to reset the boiler if you smell gas, feel unwell, or a carbon monoxide alarm is sounding.
  • Don’t use electrical switches, smoke, strike matches, or use naked flames if you suspect a gas leak.
  • Don’t keep resetting the boiler if it locks out again.
  • Don’t keep adding water if the pressure drops again soon after.
  • Don’t open the boiler casing or dismantle parts inside the boiler.
  • Don’t open random valves under or near the boiler.
  • Don’t raise the pressure above the boiler’s normal or green range.

What to do now

  1. Rule out gas or carbon monoxide danger first.
    If you smell gas, suspect carbon monoxide, or a carbon monoxide alarm is sounding, open doors and windows if you can do that without delaying getting out, move everyone into fresh air, and do not use electrical switches or flames. Turn off the gas at the meter only if it is safe, accessible, and not in a basement or cellar. For natural gas, call 0800 111 999 in England, Wales or Scotland, or 0800 002 001 in Northern Ireland. For LPG, use the emergency contact number on the tank, vessel or meter if available. If there is fire, collapse, severe breathing difficulty, or immediate danger, call 999.

  2. If there is no gas or carbon monoxide concern, pause the boiler.
    Turn the boiler off at its normal controls. If it has been running, leave it until it is cooler before judging or topping up the pressure.

  3. Check the boiler pressure gauge or display.
    Look for the pressure reading, the green area, or any error code. Many sealed heating systems are often around 1–1.5 bar when cool, but follow your boiler’s manual, label, or display if it gives a different normal range.

  4. Look for obvious water leaks before adding pressure.
    Check under the boiler, around visible pipework, near radiators, and below radiator valves. If you see dripping, wet patches, or water coming from the boiler overflow or outside pipe, stop and arrange help rather than repeatedly topping up.

  5. Make one cautious top-up only if you can clearly identify the filling control.
    A filling control may be a silver braided filling loop, a built-in lever, or a filling key, depending on the boiler. Open it slowly while watching the gauge, stop when the pressure reaches the normal or green area, then close the control firmly. If the gauge does not move, close the control and stop.

  6. Restart once and watch the gauge.
    Turn the boiler back on at its normal controls and try heating or hot water. Watch the pressure while it starts and again shortly afterwards. If the pressure rises too high, drops again, or the boiler locks out again, turn it off and get help.

  7. Contact the right person if it does not settle.
    If you own the home, contact a Gas Safe registered engineer and explain that the pressure dropped suddenly and the boiler has no heating or hot water. If you rent, report it to your landlord, letting agent, or repair service as an urgent no-heating or no-hot-water repair; include a photo of the pressure gauge and any error code, and keep a dated record of the message.

What can wait

  • You do not need to decide on a new boiler, service plan, or upgrade today.
  • You do not need to bleed every radiator right now unless a qualified person or your boiler instructions tell you to.
  • You do not need to try advanced fixes, remove panels, or keep experimenting with valves.
  • You do not need to prove the cause before asking for repair help.

Important reassurance

A sudden pressure drop is a common reason a boiler stops providing heating or hot water. The useful first step is not to solve the whole fault; it is to rule out gas or carbon monoxide danger, check the gauge, try one safe top-up if appropriate, and stop before making the problem worse.

Scope note

These are first steps only, to stabilise the situation and avoid unsafe actions. Repeated pressure loss, visible leaks, overpressure, error codes, or repeated lockouts usually need a qualified engineer to diagnose safely.

Important note

This guide is general information, not legal, medical, financial, therapeutic, engineering, or other professional advice. Boiler designs vary; if anything feels unsafe, unclear, or outside the normal user controls, leave the boiler off and contact a qualified professional.

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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