BoilerFaultCodesBoiler won't turn on? Full checklist before you call out
Before you spend £85 on a call-out, work through these nine checks. Roughly 4 in 10 "boiler won't fire" calls we see are fixable in under 10 minutes — usually something simple like a tripped fuse, dead thermostat battery, or low pressure.
Stop and call 0800 111 999 if…
You can smell gas. This is the National Gas Emergency line and it's free. Don't use switches, phones, or anything that sparks near the smell — leave the property and call from outside.
Work through these in order
Check the power
Boilers need mains power. Check the fused spur (usually near the boiler) is switched on and the fuse is intact. Try a kettle in the same socket if unsure. On modern boilers, check the display — if it's blank, you've got a power issue, not a boiler fault.
Check the consumer unit (fuse box)
Look for a tripped RCD or MCB labelled "boiler" or "central heating". Reset it once. If it trips again immediately, there's an electrical fault — stop and call an engineer.
Check the thermostat
Is the thermostat calling for heat? Turn the target temperature well above room temp (e.g. to 25°C). If it's battery powered, swap the batteries — dead thermostat batteries are the #1 "boiler won't fire" cause we see in summer.
Check the gas supply
Try another gas appliance (hob, cooker). If they don't work either, you've got a gas supply issue — phone your supplier or check if you're on a smart meter that's run out of credit.
Check the pressure
If pressure is below 0.5 bar, most boilers won't fire as a safety measure. See our repressurise guide. Pressure fault codes: Worcester E9, Vaillant F22, Ideal F1.
Check for a fault code on the display
Even a dim display can show a code. Note it down before pressing reset — resetting clears it. Search the code on this site for a plain-English fix.
Try a reset (carefully)
Hold the reset button for 3–5 seconds. On some boilers you need to press it twice within 10 seconds. Only do this if there's no obvious fault code you should note first. Never reset more than 2–3 times — repeated resets can hide a real problem and damage the boiler.
Check the timer / programmer
If you have a programmer, make sure it's not set to "off" or outside its scheduled hours. Clocks that didn't change for daylight saving are surprisingly common.
Check the condensate pipe (winter only)
In freezing weather, a frozen condensate pipe blocks the boiler from firing. See our condensate thaw guide.
Call a Gas Safe engineer if…
- › You've worked through all 9 checks and it still won't fire
- › The display shows an Emergency or lockout code (L2 / EA / F61 etc.)
- › Your fuse trips every time you reset it
- › There's water dripping from anywhere on the boiler
- › The boiler's over 10 years old and this is the second major fault in 12 months