Boiler Keeps Cutting Out? Causes & Fixes
Is your boiler firing up then cutting out? A boiler that keeps shutting down is trying to protect itself (and you) from a problem. This guide explains the common causes and which you might be able to fix yourself.
Quick Check: Is There an Error Code?
Most modern boilers display an error code when they cut out. Check your boiler's display - if there's a code showing, note it down.
See our Boiler Error Codes Guide to find out what the code means and what action to take.
If there's no error code, or the display is blank, read on for common causes.
Common Causes You Can Check Yourself
1 Low Boiler Pressure
Most common cause! If pressure drops below 1 bar, most boilers will shut down as a safety precaution.
How to Check:
- Look at the pressure gauge on your boiler
- Should read between 1-1.5 bar (usually in the green zone)
- Below 1 bar? Your boiler will cut out
How to Fix:
Top up pressure using the filling loop - see our pressure guide. If pressure keeps dropping, you have a leak that needs professional attention.
2 Frozen Condensate Pipe
In cold weather, the condensate pipe (which drains water outside) can freeze, causing the boiler to cut out.
Signs:
- Temperature is below freezing
- Boiler worked fine until it got cold
- You can see the white plastic pipe going outside
How to Fix:
Pour warm (NOT boiling) water over the frozen section of pipe to thaw it. Then reset your boiler.
3 Thermostat Issues
Sometimes the boiler is fine - it's the thermostat that's causing problems.
Check:
- Is room thermostat set higher than room temperature?
- Do wireless thermostat batteries need replacing?
- Is the thermostat in direct sunlight or near a heat source?
- Has the timer/programmer been knocked?
Causes That Need an Engineer
If the simple checks above don't solve the problem, these are likely causes that need professional diagnosis:
Ignition Failure
The boiler tries to light but fails. You might hear clicking or see the display showing ignition errors.
Causes: Faulty ignition leads, dirty electrodes, gas valve issues, blocked burner
Solution: Gas Safe engineer needed to diagnose and repair
Fan Fault
The fan creates airflow for safe combustion. If it's not working correctly, the boiler will shut down.
Signs: Boiler starts then stops quickly, no sound of fan running
Solution: Fan may need cleaning, repair, or replacement
Pump Failure
The pump circulates water through the system. If it fails, the boiler overheats and cuts out.
Signs: Radiators not getting hot, boiler overheating, gurgling sounds
Solution: Pump may be stuck (sometimes fixable) or need replacement
Overheating
If the boiler gets too hot, safety devices shut it down to prevent damage.
Causes: Pump failure, sludge buildup restricting flow, faulty heat exchanger, limescale
Solution: Needs diagnosis - could need powerflush, pump repair, or descaling
PCB (Circuit Board) Fault
The PCB is the boiler's "brain." If it's faulty, the boiler behaves erratically.
Signs: Random shutdowns, strange error codes, inconsistent behaviour
Solution: PCB repair or replacement - often the most expensive fix
Blocked or Faulty Heat Exchanger
The heat exchanger transfers heat from burning gas to water. Blockages or damage cause overheating.
Signs: Kettling noises, boiler running hot, frequent cut-outs
Solution: May need cleaning/powerflush or replacement if damaged
Boiler Still Cutting Out?
If you've tried the DIY fixes and it's still happening, call us for expert diagnosis
Should I Keep Resetting the Boiler?
Stop After 3 Resets
If you've reset the boiler 3 times and it keeps cutting out, stop resetting it.
Why? The boiler is cutting out for a reason - usually a safety feature protecting you or the boiler from damage. Repeatedly forcing it to restart can:
- Cause further damage to components
- Void your warranty
- In rare cases, create a safety hazard
It's time to call an engineer.
When Does It Cut Out?
The timing of when your boiler cuts out can help diagnose the problem:
| When It Happens | Likely Cause |
|---|---|
| Immediately on startup | Ignition failure, gas supply issue |
| After a few minutes | Overheating, pump failure, blocked system |
| When hot water is used | Diverter valve, flow sensor, low pressure |
| Randomly/intermittently | PCB fault, loose connection, thermostat |
| Only in cold weather | Frozen condensate pipe |
| When heating comes on (not hot water) | Circulation issue, sludge, pump |
Preventing Future Cut-Outs
Annual Service
Most boiler problems are preventable with annual servicing. An engineer checks all components and catches issues early.
Cost: From £105 on average for an average 3 bed home
Monitor Pressure
Check your boiler pressure monthly. Top up if it drops below 1 bar. Frequent pressure loss indicates a leak.
Magnetic Filter
A magnetic filter catches debris before it damages your boiler. Reduces risk of blockages and extends boiler life.
Insulate Condensate
If your condensate pipe runs outside, insulate it to prevent freezing in winter. We can do this during a service.
Repair Costs Guide
Approximate costs on average for an average 3 bed home - actual costs depend on your specific boiler and situation:
| Pressure top-up / basic checks | Service call (from £80) |
| Ignition electrode replacement | £120-£200 |
| Fan replacement | £200-£350 |
| Pump replacement | £200-£400 |
| PCB replacement | £350-£550 |
| Heat exchanger replacement | £400-£600 |
We always diagnose before quoting so you know the cost upfront. No hidden charges.
Need Your Boiler Fixed?
Gas Safe registered engineers serving Crawley, Horsham, Redhill, Reigate and all West Sussex & Surrey