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Homeowner guide

Your boiler has stopped working: what to do first

Many boiler stops have a simple cause you can sort out safely: the power, the settings, the pressure or, in a freeze, the condensate pipe. Anything inside the boiler is a job for a Gas Safe registered engineer.

Last reviewed 30 October 2026. General guidance, not legal advice.

First steps

  1. If you smell gas, stop. Open doors and windows, don't use switches or flames, turn the gas off at the meter if you can, and call the gas emergency line: 0800 111 999 in Great Britain, 0800 002 001 in Northern Ireland.
  2. Check the power and the gas. Is the boiler's display on? Look at its switch or fused spur, and the fuse board. On a prepayment meter, check there is credit for gas and electricity.
  3. Check the settings. Look at the timer or programmer, the room thermostat and the boiler's own heating and hot water dials. A clock change or a power cut can reset the timer.
  4. Look at the pressure. Most combi and system boilers have a pressure gauge. The maker's manual gives the right range, often about 1 to 1.5 bar when cold. If it is low, the manual shows how to top it up with the filling loop, if you are comfortable doing so.
  5. In a freeze, look at the condensate pipe. A condensing boiler drains through a plastic pipe, often outside. If it freezes, the boiler stops and may gurgle or show a fault code. Many makers say to thaw it with warm, not boiling, water, then reset the boiler.
  6. Reset once, as the manual says. Note any fault code first. If it stops again, don't keep resetting it.
  7. Call a Gas Safe registered engineer. Give the make, model, fault code and what you have tried. Look the engineer up on the Gas Safe Register before they start. If you rent, tell your landlord first: gas safety is their job.

Never open the boiler

Only an engineer on the Gas Safe Register may work on a gas boiler. Don't take the cover off, even to look. The back of the engineer's Gas Safe ID card shows the kinds of gas work they may do.

Carbon monoxide

A boiler that is not working properly can make carbon monoxide, which you can't see or smell. Headaches, dizziness, sickness or breathlessness that ease when you go outside can be a sign. Fit an audible carbon monoxide alarm. If you think you are affected, get fresh air, switch the appliance off and get medical help.

Before the engineer comes

Have ready: the boiler's make and model (on the front or under the cover flap), its age if you know it, the fault code, and when it was last serviced. Ask about the call-out charge and whether parts are extra.

Find the right trade

Sources

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Questions

Fair questions

Can I top up the boiler pressure myself?

Many boilers are designed so you can, using the filling loop. Follow the maker's manual. If the pressure keeps dropping, there may be a leak: call an engineer.

Is no hot water an emergency?

Not usually, unless someone vulnerable is at risk from the cold. A smell of gas or signs of carbon monoxide are emergencies.

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