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Date: October 20, 2021

10 Reasons why your boiler won't start

10 Reasons why your boiler won't start

Why won't my boiler start?

A broken boiler and central heating system can be really stressful. It will be impossible for you to maintain a comfortable temperature in your home or heat water with a heating system not functioning properly.

It is important that you get your boiler running quickly so you can continue with your daily routine. It is easy for you to perform just a couple of simple steps to light your boiler again. We are here to help you quickly get started by getting to the bottom of the problem and identifying the reasons for its occurrence so you can do the same.  

You may be experiencing boiler start-up issues due to some of the following issues. In order to make your boiler functional again, you can perform some basic fixes yourself.  You now need to investigate what the problem is and what we can do to fix it.

10 Reasons why your boiler won't start
10 Reasons why your boiler won't start

Burner Is Blocked

Boilers contain carbon dioxide, a gas that is produced during combustion. A burner that is clogged with carbon dioxide gas will display an erratic flame. This means you'll lack warm water or a heating system, which is especially inconvenient during winter.

This issue should be resolved by removing the carbon accumulation. There is also a possibility of it needing to be replaced in the event of breakage.

system boilers
system boilers

Low Boiler Pressure

It is possible that the boiler is not firing up because the gas pressure is not sufficient. To determine the exact cause of the gas pressure valve problem, the gas supply must be checked.

In cold weather, it's a good idea to check the meters that could have frozen due to the lower temperatures. The pressure gauge in boilers is important to check. In what proportion do you see bars? When the boiler's pressure is less than one bar, there is low pressure.

Look for the filling loop to re-pressurise the boiler. A unit's bottom usually contains this component.  Water will fill the system once the valve has been opened. The pressure indicator should increase as a result. The boiler will start again as soon as the pressure is increased. 

10 Reasons why your boiler won't start

Damaged Gas Valve

This valve regulates how much gas supply flows into and out of a system. This valve automatically opens whenever more fuel is needed for the boiler to function properly. It is possible that the boiler is not lighting due to a clogged valve, a seized valve, or a damaged wiring harness.

When a boiler's gas valve is incorrectly adjusted, it will lock out when supplied with too much gas (because it's dangerous), or too little gas (because the boiler's PCB recognises a gas supply issue)

Fan Failure

A fan starts when you turn on hot water or the heating system. Essentially, it creates a draft so that harmful gases are forced away from the boiler. A non-working fan will prevent the boiler from starting when it is needed.  In this case, it would be unwise to fire up the boiler because it is potentially dangerous.

Frozen Condensate Pipe

Excess liquid caused by condensation from your boiler is deposited outside via your condensate pipe, which runs from your boiler to (usually) the nearest outside wall.

When the weather is cold, this small amount of slowly dripping water is at risk of freezing. 

When exposed to extremely cold weather, your boilers condensate pipe can freeze. The boiler may not be able to fire up because of this, especially during the winter months.

When a condensate pipe freezes, the excess water is unable to escape and the boiler shuts down as a result. It's a surprising cause of a boiler not working.

How to fix a frozen condensate pipe

Grab a bucket of warm water and pour it over the exposed end of the pipe until the ice melts.

Thumbs up for those of you who already apply condensate pipe lagging. For less freezing troubles, ask an engineer to re-install the boiler condensate pipe internally.

The Main Fuse Box has Tripped

There are times when the system is working normally but the main fuse has blown, hindering the boiler from starting up. Check your main fuse to ensure it hasn't tripped out.

Thermostat set too low

If your thermostat is set too low it may prevent the boiler from starting. You won't be able to turn on your heating until the temperature drops below what's set on the thermostat. If this problem persists, increase the thermostat. Even when your thermostat is set lower than 21 degrees, it is possible for your boiler not to heat your home.

Pilot light not working

A malfunctioning pilot light causes the gas boiler to not ignite, which means debris has clogged the burner. It doesn't matter how small the dirt is, it can prevent the jet from working and lead to boiler ignition failure. Do not overlook even the smallest nuances. 

A pre-paid meter that does not have a credit balance

It may sound obvious but check that your prepayment meter has enough credit. Make sure all other gas-powered appliances work properly. Unless your boiler has credit, you cannot fire up your boiler if your home is fitted with a pre-paid meter. Your boiler is not malfunctioning technically.

Have you paid your gas and electricity bill? This may also seem a very obvious question, but if you have had endless bills coming out of your bank account, especially around Christmastime your account may not be as full as you think it should be. If you have no electricity or gas then your boiler will not work. Check your account and with your suppliers, there are no issues with payments.

Trapped Air in Radiators

A non-igniting boiler can signal a build-up of air inside the radiator, which leads to inefficient radiator operation. The bleeding of central heating systems and radiators consists of letting out the air.

Insert your radiator key into the valve holding a cloth underneath the catch any dripping water (this may be dirty) Rotate the key counterclockwise. You may hear a hissing or whistling sound as the air is released from the system. Once the air is all released you can close that valve.

Low Boiler Pressure

It is natural for boilers to lose pressure over time for a variety of reasons, the majority of which are not cause for concern. If your boiler is not working, and it is simply low on pressure, you will be back up and running in no time.

Find out how to restore pressure to a broken boiler. The process is simple - just check and turn. 

Are you interested in getting a boiler quote?

Troubleshooting boiler pressure issues if your boiler doesn't work


From the front of your boiler, you can see the clock-like feature of your boiler's pressure gauge. When the boilers are off, its arrow should point to the green zone - around 1 BAR.

It's also possible for your boiler pressure to be too high.

The Pilot Light has gone out

To ignite the gas and deliver heat and hot water, the boilers pilot light (the tiny internal flame) will need to be alight when your boiler is active, in order to burn the gas.

Sometimes this flame will go out, sometimes caused by draughts

In some boilers, you’ll be able to check this by peering through the casing to visually check on the boiler flame. If it’s out, you should try restarting/resetting your boiler. If the boiler is still not working, you'll need to call a heating engineer.

Boiler leaks

It's not just your carpets and floorboards that suffer from leaks within boilers or within the heating system (piping).

As we have already established, they will cause a loss of pressure that kills boilers.

What to check
Make sure that there is no standing water under your boiler (inside the case, if possible) and that the pipes are not leaking anywhere in your house, particularly the joints and bends.

Here's how to fix
A boiler engineer will check your system and either replace any faulty parts or repair any leaks in pipework that need to be repaired.

Rather than relying on eternal boiler repairs if an internal boiler part fails, you may be better off upgrading to a new boiler.

Other Boiler Problems

Besides the above problems, there are other electrical problems that could arise. As a fuel-fired boiler, it uses electrical energy to operate. Electricity problems can sometimes prevent a boiler from starting. You may have a blown fuse or a faulty electrical outlet. If you suspect an electrical fault in your boiler, call an electrician.

Aside from this, unexpected power cuts are also a common cause. It is likely that your boiler's timer resets itself if you recently had a power cut. After resetting the time zone, the program will begin to work. Neither a breakdown nor a malfunction has been observed. There are times when a simple reset is all that an appliance needs.

There may be any number of reasons why a boiler does not ignite. There are times when you can fix the problem yourself. You might need to seek the assistance of a gas-safe engineer in other cases.

You need to ensure you get your boiler and any other gas appliances like fires, ovens, hobs, etc. serviced by a qualified gas safe registered engineer annually. This is not only to keep the appliances in full working order maintenance-wise but also to safety check them for a boiler leak or gas leak which can be fatal.

If you are at all unsure or you think the problem could be something else then please give Danum Plumbing & Heating a call. We are happy to check anything you are unsure of to maintain the safety of your home.

10 Reasons why your boiler won't start

10 Reasons why your boiler won't start

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