How to Reset a Boiler (and When Not To)

To reset a boiler, find the reset button or reset option on the control panel (your manual shows where it is), press or hold it as the manual describes, and wait for the boiler to try to start again. Before you do, check that the gas is on, the pressure gauge is in the normal zone and, in freezing weather, that the condensate pipe outside is not frozen. A reset only restarts the boiler. It does not fix whatever made it shut down, so if it locks out again, stop pressing the button and book an engineer.

What a Lockout Actually Is

A boiler locks out when one of its safety systems detects a problem and shuts it down. It might have tried to light and not detected a flame, sensed low water pressure, overheated, or found the condensate drain blocked. The boiler then waits for a manual reset instead of trying again on its own, which is deliberate. You will usually see a fault code, a flashing light or a message on the display.

Fault codes differ between manufacturers, so check the manual for your model. We service all the main makes, including Vaillant, Worcester Bosch, Baxi and Ideal.

Checks to Make Before You Reset

Is the gas getting through?

Try another gas appliance, such as the hob. If that won't light either, the problem is the gas supply rather than the boiler. On a prepayment meter, check there is credit. Check the gas isn't turned off at the meter. If you smell gas at any point, don't reset anything: leave the property, don't operate switches, and call the National Gas Emergency number on 0800 111 999.

Is the pressure in range?

Look at the pressure gauge. If it has dropped below the normal zone, the boiler may have shut down to protect itself and a reset won't help until the pressure is back up. Our guide to repressurising a boiler safely walks through it. If the pressure keeps falling after you top up, read why a boiler loses pressure.

Is the condensate pipe frozen?

Condensing boilers send waste water out through a plastic condensate pipe, which often runs outside. In very cold weather it can freeze, the water backs up, and the boiler locks out. Sometimes you can hear gurgling from the boiler. Pouring warm (not boiling) water along the outside section of the pipe usually thaws it. Only do this if the pipe is at ground level and easy to reach safely.

Is it the controls rather than the boiler?

If there is no fault code and the boiler simply isn't coming on, check the thermostat, timer and programmer first. A flat battery in a wireless thermostat or a programmer showing the wrong time can look exactly like a broken boiler. See thermostat and timer problems that aren't actually boiler faults.

How to Reset the Boiler

1. Note the fault code. Write it down or take a photo before you do anything. An engineer will want to know it, and it can disappear after a reset.
2. Find the reset control. It might be a button marked with a reset symbol, a button you hold for a few seconds, or an option in a menu on digital displays. The manual shows which.
3. Reset once, as instructed. Press or hold the control as the manual says, then wait. The boiler should go through its start-up sequence and light.
4. Check the heating and hot water. Run a hot tap and put the heating on to make sure the boiler is firing properly.

Some models also recover after being switched off at the fused spur on the wall, left for a short while and switched back on. Only do this if your manual suggests it.

When Not to Keep Resetting

If the boiler locks out again, whether straight away or a few hours later, stop. Manufacturers limit how many times you should try, and repeatedly resetting a boiler that keeps shutting down means repeatedly asking it to run with a fault its safety system has already detected. Call an engineer instead if:

• The boiler locks out more than once.
• You can smell gas or see signs of scorching, soot or discolouration around the boiler.
• The flame looks yellow or orange rather than blue, on a boiler where you can see it.
• The same fault code keeps coming back.
• The boiler makes banging or unusual noises before it shuts down.

Never remove the boiler casing to try to find the fault yourself. Any work inside a gas appliance has to be done by a Gas Safe registered engineer, and you can check an engineer is Gas Safe registered before they start.

Why Lockouts Are Often a Servicing Issue

Many of the causes behind lockouts build up gradually: a dirty burner or electrode that struggles to light, a partly blocked condensate trap, an expansion vessel slowly losing its charge. These are exactly the things an annual boiler service checks and cleans. A boiler that has missed a service or two is more likely to start locking out, and it tends to happen on the first cold week of the year.

If your boiler has started locking out, or it is due its service anyway, get in touch with the make, model and fault code. We'll book a Gas Safe engineer and quote before any work beyond the visit goes ahead.