Why won't my boiler turn on?
A boiler that will not fire up is often down to a handful of simple causes you can check yourself. Here is the order to work through before calling an engineer.
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Upfront cost — no obligation If your boiler will not turn on, start with the simple things — the power supply, the thermostat, the pressure, the gas supply and, in cold weather, a frozen condensate pipe. Many no-start problems come down to one of these and can be sorted in a few minutes. This guide walks through the checks in order, and points to the right fix when the cause is inside the boiler.
Check the power, thermostat and timer
First make sure the boiler has power — check it is switched on at the fused spur, and that a fuse has not blown or a switch been knocked off. Then check the room thermostat is turned up and calling for heat, and replace the batteries if it is wireless. Finally check the programmer or timer is set to come on and is showing the right time. A surprising number of no-start calls come down to a setting or a flat battery.
First make sure the boiler has power — check it is switched on at the fused spur, and that a fuse has not blown or a switch been knocked off.
Check the boiler pressure
Look at the pressure gauge on the front of the boiler. If it is below 1 bar, the boiler may lock out and refuse to fire to protect itself. Topping the pressure back up to around 1 to 1.5 bar often gets it going again — our boiler pressure guide explains exactly how. If the pressure keeps dropping, there is an underlying fault that needs an engineer.
In cold weather, check for a frozen condensate pipe
If the boiler stopped overnight in freezing weather and is showing a fault or gurgling, the most likely cause is a frozen condensate pipe. This is common on the first cold mornings of winter and is often a simple fix — see our frozen condensate pipe guide for how to thaw it safely. Also check your gas supply is on and, if you have a prepayment meter, that you are in credit.
If the boiler stopped overnight in freezing weather and is showing a fault or gurgling, the most likely cause is a frozen condensate pipe.
When to call a Gas Safe engineer
If the power, thermostat, pressure, gas supply and condensate pipe are all fine and the boiler still will not fire, the fault is likely inside the boiler — a faulty ignition, fan, PCB or gas valve, none of which are DIY repairs. At that point, call a Gas Safe engineer. Our boiler repair team can diagnose and fix it, and we offer an emergency call-out if you have no heating in cold weather.
If the power, thermostat, pressure, gas supply and condensate pipe are all fine and the boiler still will not fire, the fault is likely inside the boiler…
Frequently Asked Questions
Why won't my boiler turn on?
The most common causes are no power to the boiler, a thermostat or timer set wrong, low pressure, a frozen condensate pipe in cold weather, or no gas supply. If those are all fine, the fault is usually inside the boiler.
Why has my boiler stopped working in cold weather?
In freezing weather the usual cause is a frozen condensate pipe, which blocks and shuts the boiler down. Thawing the external pipe with warm water often restarts it.
My boiler has no power — what should I check?
Check it is switched on at the fused spur, that no fuse has blown, and that no switch has been knocked off. If the display is still dead, an engineer should check the supply and the boiler.
Should I keep trying to reset my boiler?
Reset it once following the manual. If it locks out again, stop and call an engineer, as repeatedly resetting can hide a fault that needs fixing.
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