Boiler Won't Turn On? 5 Things to Check Before You Call for Repair

Most of these won't fix a genuine fault, and that's fine - the point isn't to avoid calling an engineer, it's to rule out the handful of things that are genuinely a two-minute check, and to arrive at that call with useful information instead of just "it's not working."

1. Check the pressure gauge

With the heating off and the system cold, most domestic boilers should read between 1 and 2 bar. Below 1 and the system has lost pressure somewhere - many boilers won't fire at all below a certain threshold. There's usually a filling loop to top it up yourself, but if it keeps dropping back down afterwards, that's a leak somewhere in the system and worth reporting as exactly that when you call.

2. Check the thermostat is actually calling for heat

It sounds obvious, but a thermostat set below room temperature, a dead battery in a wireless unit, or a smart thermostat stuck on an old schedule will all stop a perfectly working boiler from firing. Confirm the display is on, the target temperature is genuinely above the current room temperature, and it's set to heat rather than off or holiday mode.

3. Check the fuse board or isolator switch

Boilers run on electricity as well as gas, and a tripped circuit or a knocked isolator switch near the boiler will stop it dead with no fault code at all. Check the consumer unit for a tripped switch, and confirm the boiler's own isolator (usually a switched fused spur nearby) hasn't been knocked off.

4. Check for a frozen condensate pipe

In cold weather, this is the single most common cause of a boiler locking out. If the external condensate pipe is accessible, thawing it with a warm (not boiling) cloth or a hot water bottle often resolves it - covered in more detail in our guide to what counts as a boiler emergency.

5. Check the display for a fault code

Modern boilers show a code or symbol when something's wrong rather than just going silent. It's worth noting down exactly what's displayed before calling - different brands use different codes, and having it ready means an engineer can often narrow down the likely cause before even arriving.

If none of this fixes it

That's genuinely the expected outcome for most real faults - these checks rule out the quick causes, not the ones that need a Gas Safe registered engineer. See our Emergency Boiler Repair page or call 07472 251465.