Boiler Not Working – Won’t Fire
Causes, Safe Checks & What To Do
When a boiler won’t fire, it’s rarely “random.” Modern boilers are safety-driven machines. If something isn’t right — gas, water pressure, ignition, airflow, controls, or sensors — the boiler will refuse to light to protect the appliance and your home.
This guide explains why boilers stop firing, what the problem usually means, what you can safely check yourself, and when the fault needs a Gas Safe engineer.
This page covers the big picture. Each specific fault is explained in detail in the linked guides below.
What “boiler not working” or “won’t fire” actually means
A boiler “firing” means the burner ignites and stays lit long enough to heat water safely.
If your boiler:
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clicks but doesn’t light
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lights briefly then shuts down
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has power but no heat
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shows a fault or lockout
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works intermittently
…it means one or more safety conditions hasn’t been met.
Boilers don’t fail silently. They stop because something upstream or downstream is wrong.
The most common reasons a boiler won’t fire
1. Low system pressure
One of the most common causes we see.
If pressure drops too low:
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the boiler cannot circulate water
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sensors prevent ignition
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the boiler may lock out
Pressure loss usually points to:
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a small system leak
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recent bleeding of radiators
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expansion vessel or PRV issues
2. Ignition failure (clicking but no flame)
If you hear clicking but no flame appears, ignition has been attempted but failed.
Common reasons:
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gas supply interruption
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faulty ignition electrode
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dirty burner
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flame sensing failure
The boiler will stop firing after a few attempts to prevent unsafe ignition.
3. Boiler has power but won’t ignite
Lights on, display working — but no heat.
This usually means:
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a safety sensor is blocking ignition
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airflow or flue checks have failed
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internal temperature or pressure readings are out of range
This is not an electrical power issue — it’s a logic lock.
4. Lockout condition
A lockout means the boiler has detected repeated failed ignition or unsafe conditions and has shut itself down.
Lockouts are common after:
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pressure loss
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gas interruptions
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ignition failures
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frozen condensate pipes
Resetting without fixing the cause often leads to repeat lockouts.
5. After a power cut
Power cuts can:
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disrupt boiler logic
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reset internal controls
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cause ignition or sensor faults on restart
Some boilers need a controlled reset sequence to fire again safely.
6. Frozen condensate pipe (cold weather)
In freezing weather, condensate pipes can freeze, preventing safe drainage.
When this happens:
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the boiler will refuse to fire
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fault codes often appear
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ignition is blocked to prevent internal flooding
7. Heating or hot water missing (but not both)
If:
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hot water works but heating doesn’t
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or heating works but hot water doesn’t
This usually points to:
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diverter valve issues
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control or programmer faults
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zone valve or sensor problems
Safe checks you can do (without tools)
You can safely check:
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boiler pressure gauge (usually 1.0–1.5 bar cold)
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power supply and fused spur
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thermostat and programmer settings
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visible fault codes on the display
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gas supply to the property (other appliances working)
You should not:
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remove boiler casing
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interfere with gas components
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repeatedly reset a locking boiler
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top up pressure repeatedly without understanding why it’s dropping
If the boiler keeps stopping, there’s an underlying fault.
Why boilers refuse to fire (engineer insight)
From an engineer’s point of view, most “won’t fire” calls fall into patterns:
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pressure instability
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ignition sequence failure
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safety sensor disagreement
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blocked condensate or airflow
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control logic preventing unsafe startup
Boilers are designed to fail safe, not “try harder.”
That’s why the correct fix isn’t forcing resets — it’s identifying which safety condition isn’t being satisfied.
When to call a Gas Safe engineer
Call an engineer if:
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the boiler repeatedly locks out
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pressure keeps dropping
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fault codes return after reset
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there’s no ignition despite power
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the boiler stops firing intermittently
These faults won’t resolve themselves and can worsen if ignored.
Related boiler fault guides
For detailed explanations of specific situations, see:
Each guide explains the exact fault logic, symptoms, and proper resolution.
Key takeaway
A boiler that won’t fire is protecting itself — and you.
The solution isn’t guessing or repeated resets.
It’s understanding what condition the boiler is refusing to accept.
If your boiler still is’nt working, it’s likely time for a clear diagnosis by a Gas Safe engineer.
Boiler Not Working / Won’t Fire – FAQs
Why has my boiler suddenly stopped firing?
When a boiler stops firing, it’s usually because one of its safety conditions hasn’t been met. That might be low system pressure, no gas supply, a frozen condensate pipe, or the boiler not receiving a clear demand from the controls. Boilers are designed to shut down rather than run in unsafe conditions.
The boiler has power, but won’t ignite — what does that actually tell me?
Having power only means the boiler electronics are live. It doesn’t mean ignition is allowed. If the boiler won’t ignite, it’s often because a safety check has failed — such as insufficient water pressure, airflow problems, ignition sensing issues, or a lockout caused by a previous fault.
What boiler pressure will stop a boiler from firing?
Most boilers need roughly 1.0–1.5 bar when cold to operate normally. If pressure drops too low, the boiler may refuse to fire to protect the heat exchanger and pump. If pressure keeps dropping after topping up, there’s likely an underlying leak or system fault.
Is resetting the boiler a safe thing to try?
Trying one reset is usually safe and often recommended by manufacturers. If the boiler locks out again, repeated resets should be avoided. Multiple resets don’t fix faults and can sometimes delay proper diagnosis or make a problem worse.
Can cold weather stop a boiler from firing?
Yes. In winter, frozen or partially blocked condensate pipes are one of the most common causes of boilers failing to ignite. The boiler may attempt to start, then shut down repeatedly, or display a lockout fault.
My boiler clicks or tries to start but no flame appears — why?
This usually means the boiler is attempting ignition but failing to establish a flame. Causes can include gas supply issues, ignition or flame-sensing problems, or airflow and flue safety checks failing. These faults need proper testing rather than guesswork.
Could the problem be gas supply rather than the boiler itself?
Yes. If gas pressure is low or the supply is interrupted, the boiler will not fire. If other gas appliances are also affected, the issue may lie with the gas meter, regulator, or supply. Any suspicion of a gas problem should be treated seriously.
When should I stop troubleshooting and call a Gas Safe engineer?
You should stop and call an engineer if there’s a gas smell, repeated lockouts, loud bangs, water leaking onto electrics, electrical tripping, or concerns about the flue. These signs indicate faults that should not be handled without proper training and equipment.