Boiler Problems
Boiler Not Turning On? Causes and Safe Checks
Reviewed by our Gas Safe registered engineers · Last updated 21 July 2026
A boiler that won’t turn on usually comes down to a few things — no power, low pressure, or a thermostat that isn’t calling for heat. Here’s how to tell them apart safely, and when it’s time to call a Gas Safe engineer.
Quick answer: If there’s no display at all, it’s usually a power problem — check the fused spur and your consumer unit. If the display is on but the boiler won’t fire, it’s most often low pressure (top it back up to around 1.3 bar) or the thermostat not calling for heat. Repeated ignition lockouts, or anything involving a gas smell, need a Gas Safe engineer.
Common Causes
Why a boiler won’t turn on
These are the causes we’re called out for most often, roughly in order. The colour on the left of each row shows whether it’s usually a safe homeowner check or a job for an engineer.
| What you see | Likely cause | What to do |
|---|---|---|
| No display or lights at all | No power — tripped fuse, RCD or spur | Check the fused spur and consumer unit; reset the RCD once |
| Display on, won’t start | Low pressure lockout | Check the gauge; repressurise to ~1.3 bar via the filling loop |
| Thermostat blank or silent | Flat batteries or wrong schedule | Replace the batteries; check the programmer is calling for heat |
| Clicks but won’t ignite | Ignition or gas supply fault | Check other gas appliances work; if not, book an engineer |
| Dead after a power cut | Programmer or PCB fault | Switch off at the spur for 60 seconds; if still dead, needs an engineer |
| Nothing in cold weather | Frozen condensate pipe | Thaw the external white pipe with warm water, then reset |
Safe Checks
What you can safely check yourself
Safe to check
- The fused spur next to the boiler is switched on and the fuse hasn’t blown
- The pressure gauge reads around 1–1.5 bar (top up to ~1.3 if low)
- The programmer/thermostat is set to come on and its batteries are fresh
- In winter, the external condensate pipe hasn’t frozen
Stop and call us if…
- You can smell gas — leave the property and call 0800 111 999
- The boiler locks out again straight after a reset
- There’s water leaking from the boiler or any scorching
Engineer Insight
What we usually find
Across North London, a boiler that’s completely dead is far more often an electrical supply issue — a tripped spur or a blown fuse — than a boiler fault. If the display works but it won’t fire, pressure and ignition are the usual culprits. We always check the simple, free things first, so you’re never paying for parts you don’t need.
Costs
What repairs typically cost
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
Boiler won’t turn on — your questions answered
Why has my boiler suddenly stopped working?
The most common causes are a tripped fuse or spur, low system pressure, or a thermostat that isn’t calling for heat. Checking those three covers the majority of ‘dead boiler’ call-outs we attend.
My boiler has power but won’t fire — what now?
Check the pressure gauge first. If it’s below about 1 bar, top it up to 1.3 bar using the filling loop. If pressure is fine, make sure the thermostat or programmer is actually calling for heat.
Could a power cut have stopped my boiler?
Yes. After a power cut the programmer can lose its schedule or the PCB can trip. Turn the boiler off at the fused spur for 60 seconds, then back on. If it stays dead, it needs an engineer.
Is a boiler not turning on an emergency?
Not usually. But if you can smell gas, leave the property and call the Gas Emergency Service on 0800 111 999. Loss of heating in very cold weather with vulnerable occupants should be treated as urgent.
How much does it cost to fix?
A diagnostic visit is typically £80–£120 in North London. The repair itself depends on the fault, from a simple reset to a PCB replacement. You’ll always get an upfront quote before we proceed.
Related
Keep troubleshooting
When the boiler tries to fire but locks out — ignition, flame and gas causes.
Read guideBoiler ProblemsBoiler Flashing a Warning LightWhat the flashing light or code on your boiler is trying to tell you.
Read guidePressureLow Boiler PressureWhy the pressure reads low and how to bring it safely back to normal.
Read guidePressureHow to Repressurise a BoilerStep-by-step: using the filling loop to top your boiler back up to 1.3 bar.
Read guideBoiler ProblemsBoiler Keeps Switching OffShort-cycling and lockouts — pressure, sensors and the usual triggers.
Read guideFault CodesBoiler Fault Code LibraryLook up your exact code by brand — Worcester, Vaillant, Ideal and more.
Browse codesBrowse all Boiler Problems guides, or head back to the Help & Advice Centre.
Still won’t turn on? We’ll get to the bottom of it.
Book a Gas Safe engineer for a proper diagnosis, or call and tell us exactly what the boiler’s doing — we’ll give you an honest steer before anyone comes out.
Gas Safe Registered 918817 | North London specialists | Upfront pricing