Before you call an engineer because your boiler isn’t working, it’s worth ruling out a few common, safe-to-check causes: power, thermostat and timer settings, pressure, and a simple reset.
Many “boiler not working” call-outs turn out to be one of these quick fixes rather than a fault with the boiler itself.
That said, a small number of warning signs mean you should stop immediately and contact a Gas Safe registered engineer rather than attempt anything yourself, and this guide covers those first.
Stop and call immediately if you notice any of these
Do not attempt any of the checks further down this article, and do not operate any electrical switches, if you notice:
- A smell of gas, near the boiler, meter or pipework.
- A carbon monoxide alarm sounding.
- A visible water leak, especially near electrical components or wiring.
- Soot or dark staining, or a lazy yellow/orange flame where the pilot light or burner should be blue.
According to the Gas Safe Register, if you smell gas or suspect a leak: get fresh air immediately by opening doors and windows, turn off the gas at the meter (unless the meter is in a basement or cellar), put out any naked flames, don’t smoke, and don’t operate light switches or other electrical switches, since this can ignite escaping gas.
Then call the National Gas Emergency Service on 0800 111 999. If anyone is experiencing symptoms such as headaches, dizziness, nausea, breathlessness or confusion, treat this as a possible carbon monoxide exposure, get outside into fresh air, and seek medical help.
Quick reference: common causes and what to check
| Symptom | Possible cause | Safe to check yourself? |
|---|---|---|
| No power, blank display | Fuse, tripped circuit breaker, or boiler switched off | Yes |
| Boiler on, but no heat | Thermostat or timer not calling for heat | Yes |
| Pressure gauge low (below 1.0 bar) | Water lost from the system, needs topping up | Yes, usually |
| Fault code or flashing light | Depends on the code; some clear with a reset, others need an engineer | Sometimes |
| Pilot light not blue, or won’t stay lit | Possible ventilation, flue or combustion issue | No, stop and call an engineer |
| No hot water or heating after a cold snap | Frozen condensate pipe | Partially, see below |
Check the power supply
If the display is completely blank, check that the boiler is switched on at the wall, that the plug hasn’t worked loose, and that the relevant fuse hasn’t blown or the circuit breaker tripped at your consumer unit. If other electrical appliances in the house are also affected, the issue is likely a wider power problem.
Check your thermostat and timer
A boiler with no power fault can still fail to fire simply because the controls aren’t asking it to.
Make sure your thermostat is set above the current room temperature, and check that your timer or programmer is set to have the heating on, rather than off or on hold. If your thermostat is wireless, check its batteries, since these can cause the same symptom as a genuine fault.
Check the boiler pressure
Most UK sealed systems should read around 1.0 to 1.5 bar when the system is cold. If your gauge reads below this, many boilers will refuse to fire as a safety measure.
You can usually top this up yourself using the filling loop: turn the boiler off, open the valve(s) slowly until the gauge reads around 1.0–1.5 bar, then close them firmly and turn the boiler back on.
If the pressure keeps dropping after topping up, this usually points to a leak and will need to be checked by a Gas Safe engineer rather than repeatedly topping up.
Try a reset, if there’s no fault code stopping you
On most boilers there’s a clear reset button, either visible on the front panel or behind a flap, and simply resetting can sometimes resolve a heating or hot water issue.
Check your manual for your specific model’s reset procedure, since this can vary. If a fault code is displayed and reappears after resetting, don’t keep repeating the reset: note the code and contact a Gas Safe registered engineer, since continuing to reset without addressing the underlying issue can, in some cases, make things worse.
Check for a frozen condensate pipe (in cold weather)
In freezing conditions, the condensate pipe, which carries waste water from the boiler to an outside drain, can freeze and block, causing the boiler to shut down.
Common causes include the pipe freezing at its most exposed point, or a blockage further along the line, such as leaves or moss at an external drain.
If you can see visible ice on the external pipe, this is worth flagging as a likely cause, but thawing it safely (for example, avoiding boiling water, which risks cracking the pipe or scalding) is something to check your specific boiler’s manual for or ask an installer about, rather than following generic instructions, since pipe layout and material vary by installation.
When to stop and call a Gas Safe engineer
Beyond the immediate emergency signs above, book an engineer rather than continuing to troubleshoot if:
- The pilot light or flame is any colour other than blue.
- Pressure keeps dropping repeatedly after topping up.
- A fault code reappears after a reset.
- You’re not confident locating or operating the filling loop, reset button, or fuse box.
- The boiler has gone a full year or more without service, since annual servicing by a Gas Safe registered engineer is the main way faults are caught early.
You should never attempt to open the boiler casing or carry out repairs yourself; this work should always be carried out by a Gas Safe registered engineer.
If you’re a tenant or landlord
A boiler that’s stopped working in a rented property is the landlord’s responsibility to repair, not the tenant’s. Tenants should report the fault promptly, especially if any of the emergency signs above are present, rather than attempting checks themselves.
Landlords are legally required to keep heating installations in proper working order and to have gas appliances safety-checked annually by a Gas Safe registered engineer.
Frequently asked questions
A single reset is generally fine. If the same fault code reappears, stop resetting and call an engineer, since repeatedly resetting without addressing the cause can risk further damage.
This points towards a specific component fault, such as a valve or a control setting, rather than a total system failure. It is worth noting for whoever diagnoses it, though the cause itself needs a Gas Safe engineer to confirm.
Sometimes, but check your boiler’s manual or ask your installer first, since the wrong approach (for example, using boiling water) can crack the pipe.
An annual service by a Gas Safe registered engineer is the standard recommendation for keeping a boiler running safely and catching faults early.
Sources
- Gas Safe Register, What To Do in a Gas Emergency (https://www.gassaferegister.co.uk/gas-emergency/what-to-do-in-a-gas-emergency/)
- Gas Safe Register, Carbon Monoxide Poisoning: CO Symptoms & Prevention (https://www.gassaferegister.co.uk/gas-safety/carbon-monoxide-poisoning/)
- Landlord and Tenant Act 1985, Section 11, legislation.gov.uk (https://www.legislation.gov.uk/ukpga/1985/70/section/11)
- Shelter England, Heating, hot water and power problems (https://england.shelter.org.uk/professional_resources/legal/housing_conditions/responsibility_for_repairs/heating_hot_water_and_power_problems)
Accurate as of: 8 August 2026