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Why does my boiler keep turning off?
A boiler that keeps cutting out is usually protecting itself. Low pressure, the thermostat and a frozen condensate pipe are things you can check. The rest need an engineer.
- 1 to 1.5bar when cold, for most boilers
- 4things you can check yourself
- £120repair visit if it’s a fault
4quick checks
A boiler that keeps switching itself off is frustrating, but it’s usually doing its job. When a boiler detects something wrong, it shuts down to stay safe. The manufacturers call it a lockout.
The trick is working out what it’s protecting itself from. Some causes you can check and fix in a few minutes. Others need a Gas Safe registered engineer.
Things you can check
Start here before you book anyone.
The pressure
Low pressure is one of the most common reasons a boiler cuts out. With the boiler cold, the gauge should read around 1 to 1.5 bar. Check your manual for your boiler’s exact range. Topping up through the filling loop doesn’t need an engineer.
The thermostat and timer
Make sure the thermostat is set above the room temperature, the batteries are good, and it’s not sitting next to a radiator or in the sun. Check the timer after the clocks change.
The condensate pipe
In a frost, a frozen condensate pipe will shut the boiler down, often with gurgling. Our frozen condensate guide shows you how to thaw it.
The gas supply
If the hob doesn’t light either, check the meter. A prepayment meter that’s run out needs turning back on, and the boiler may then need a reset.
Pressure check
Things for an engineer
If the checks don’t sort it.
- A faulty pump, often with a droning noise
- Overheating or kettling, often with banging
- Sludge restricting the water flow
- Ignition faults or a blocked burner
- A blocked heat exchanger, flue or fan
These are inside the boiler or the system, and the casing should only come off for a competent engineer.
Why servicing matters here
Vaillant points out that a boiler left unserviced can start switching off at random. A yearly service can catch many of these before they stop your heating.
Checking the water
Fix the cause before you reset
Resetting a boiler without fixing the cause just puts it back into lockout. If it won’t start, or the fault code stays, call a Gas Safe registered engineer.
What you notice and what it usually means
| Likely cause | Who fixes it | |
|---|---|---|
| Pressure gauge below 1 bar | Low pressure | You, with the filling loop |
| Cuts out in a frost, gurgling | Frozen condensate pipe | You, if the pipe is at ground level |
| Hob won’t light either | Gas supply or meter | You, or your gas supplier |
| Heating goes off too early | Thermostat or timer | Usually you |
| Droning noise | Pump | An engineer |
| Banging or kettling | Overheating, sludge or scale | An engineer |
| Fault code that won’t clear | A fault that needs diagnosing | An engineer |
What should I do next?
- Pressure below 1 barTop it up
Our guide shows how.
- Code on the displayLook it up
The common ones explained.
- Still cutting outBook a repair visit
£120 including VAT, before any parts.
- Not serviced this yearBook a service
£120 including VAT.
Common questions
Why does my boiler keep turning off?
It’s usually a safety shutdown, called a lockout. The common causes are low pressure, a frozen condensate pipe, a problem with the gas supply, the thermostat, or a fault such as a failing pump.
How often should I have to reset my boiler?
Hardly ever. One reset after you’ve fixed a cause, like topping up the pressure, is fine. If you’re resetting it regularly, there’s a fault, and it needs a Gas Safe registered engineer.
Can low pressure make a boiler cut out?
Yes. Most boilers switch off when the pressure drops too low. Top it up to around 1 to 1.5 bar with the boiler cold. If it keeps dropping, there’s a leak somewhere.
Why does my boiler come on then go off after a few minutes?
It can be the thermostat being satisfied quickly because it’s in a warm spot, or the boiler overheating because water isn’t moving properly, from a pump fault or sludge. If the thermostat isn’t the answer, book a repair.
Can sludge make a boiler cut out?
Yes. Sludge restricts the water flow, so the boiler overheats and shuts down. A magnetic filter cleaned at each service helps keep it out.
Is it covered by Home Care?
Breakdown repairs to the boiler are covered on the Home Care Boiler and Complete plans, with parts and labour included, Monday to Friday. Faults that were there before you joined, and damage caused by sludge or scale, aren’t covered.
Related pages
Sources: Vaillant, how to reset a boiler; Vaillant, most common boiler problems; Worcester Bosch, boiler pressure. Checked 2 November 2026.
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