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10 Reasons Why Your Oil Boiler is Not Firing Up


Every homeowner dreads waking up to a malfunctioning boiler that won’t fire up. This is particularly the case in winter when you are hugely dependent on your boiler for central heating and domestic use. However, oil boilers are programmed to lock out when they have internal faults that might damage components of the boiler or pose a safety risk if the boiler were to continue operating. As such, you would inevitably experience a boiler that won’t fire up at least once in the lifetime of your boiler.

In this guide, we explore some of the most common reasons that may lead to a boiler lockout, therefore, resulting in a boiler that won’t fire up. Some of these reasons are simple, and you can resolve them on your own, while some might be a little more complicated, and you might have to call in a professional OFTEC engineer.

Boiler lockouts and misfiring boilers

As earlier said, when your oil boiler detects a serious internal fault, it would initiate a lockout and won’t fire up until you reset the boiler or resolve the internal issue. Although a lockout is meant to protect you and the boiler, it can be hugely inconvenient were it to happen on a cold day when you are particularly in need of central heating and hot water.

To tell whether your oil boiler is refusing to fire up due to a lockout, check the boiler’s display panel where an error or fault code would be displayed. Alternatively, the boiler would be flashing a coloured light. And once you have established that the boiler is in lockout mode, you can reference the displayed fault code on your boiler manual and decide whether or not an OFTEC engineer is needed.

If it is a simple issue, a simple reset will clear it, and you will be back enjoying central heating and hot water in no time. Most oil boilers can be reset by long-pressing a button, but it would be best to consult your manual on how to perform a boiler reset. However, boiler rest will not resolve all boiler lockout issues, and your boiler may refuse to fire up even after you have reset it.

Why oil boiler is not firing up and their fixes

The boiler has run out of fuel

The simplest and most common reason your oil boiler won’t fire up for central heating and domestic hot water is that it has run out of fuel. As such, if your boiler is in peak condition, then it suddenly refuses to fire up; the first thing to check would be the level of heating oil in the storage tank.

You can check the level of heating oil in your storage tank by reading the electronic gauge that is usually located on the oil tank or installed somewhere in your house. Alternatively, you can ascertain the oil level by dipping a stick into the tank.

The fix

If your oil tank is empty or a small amount of oil is left at the bottom, then insufficient oil is likely to be the cause of the boiler misfiring incident. You will, therefore, have to call your regular oil supplier and request them to refill your oil tank. If they are unavailable at the moment, you can get oil from another company that offers top-up services as you wait for your leading supplier to be available. This will, however, cost you more than what you usually spend to refill your oil tank.

On the other hand, if the tank still has sufficient oil, but the fault code on the display panel indicates an oil supply issue, then there might be debris at the bottom of the tank. And if this is the case, you will need to plan for the oil tank to be cleaned once the current oil supply runs out.

The boiler has no power

Regardless of their fuel type, most modern boilers require a small amount of electricity for ignition. Your oil boiler isn’t exempt from this and will require electricity to fire up. Suppose there is no electricity in your house or the electrical supply to the boiler has been interrupted; your boiler won’t fire up until the issue is resolved and the electricity supply is restored.

Some of the possible reasons why your boiler might not have power include:

  • There is a power outage in the neighbourhood caused by harsh weather conditions such as heavy rainfall, snow, lightning, or strong winds
  • The boiler was accidentally turned off
  • The circuit is overloaded, and the circuit breaker has tripped
  • Your home has attained the preset temperature as per the thermostat settings

The fix

There are several ways to resolve the issue of an oil boiler not firing up due to power issues. Some of these fixes include:

  • Resetting the boiler by pressing and holding the reset button for 10 seconds
  • Turning on the isolation switch next to the boiler if it were accidentally turned off
  • Flicking the fuse box switch back on, it had tripped.
  • Waiting for power to be restored

Incorrect boiler pressure

If your boiler’s pressure is too high or too low, the boiler will initiate a lockout, and you will have to adjust the pressure before you can reset the boiler. It is worth noting that although most boilers are designed to operate at an optimum pressure of 1.3 bar, they can still comfortably run at pressures ranging from 1-3 bar.

The fix

If your boiler’s pressure is too high, say, around 3-bar, you will need to bleed water from the system until the pressure gauge reads a pressure of 1.3 bar. And to do this, you will need to locate the drain cock or a radiator valve and bleed out air and water from the system.

On the other hand, if your boiler’s pressure is too low, say, below 1 bar, you will need to repressurize the system by topping it up with water. But before you can do this, first check the system for leaks, as topping up a leaking system may result in severe water damage to your property.

Once you have ascertained that there are no leaks in the system, open the valve on the external filling loop and add water to the system until the pressure rises to about 1.3 bar.

Blocked or frozen condensate pipe

All boilers have a condensate pipe that vents waste condensed gases outside your property. As these pipes are usually exposed to the harsh outside weather, they are prone to freezing, especially if external temperatures are below -2°C. They can also be blocked by debris such as soil and leaves. And when the boiler sensor detects that the condensate pipe is clogged or frozen, it will initiate a lockout to protect the system and your property from damage.

The fix

To resolve this issue, you first have to locate the condensate pipe and ascertain whether it is obstructed or frozen. The condensate pipe is easy to identify as it is a small white 21.5 mm pipe protruding out of your property at the wall closest to the boiler. If the pipe is obstructed by debris, you can remove the debris and attempt to reset the boiler.

On the other hand, if the condensate pipe is frozen, you have to thaw it with lukewarm water. You should, however, be careful not to use hot water as it might cause the pipe to crack. Once the ice in the pipe has thawed, a simple reset will clear the error code on your display panel, and your boiler will fire upon the next attempt.

Faulty fan

The boiler fan plays a crucial role in the boiler in that it pushes the harmful gases generated by the boiler down the flue pipe. If the fan develops an issue, the boiler will initiate a lockout as it would be dangerous to operate with a malfunctioning fan.

The fix

A faulty fan is easy to diagnose as the boiler makes small humming noises and vibrates when in operation. Depending on the seriousness of the fault, you may have to get your boiler’s fan repaired or replaced. Owing to the project’s complexity, this is something that you won’t be able to do yourself, and you will need to call in a professional heating engineer.

Faulty air pressure switch

The air pressure switch detects whether the boiler fan is working by comparing the air pressure in the boiler and the flue. If the fan isn’t running yet the boiler is on, the air pressure switch would relay the information to the PCB unit, initiating a lockout as it would be unsafe to operate with a malfunctioning boiler.

If the air pressure switch is faulty, it might not detect when the fan is up and running and convey the wrong message to the PCB unit. The boiler would then go into lockout and would refuse to fire up.

The fix

Similar to the issue with a faulty fan, a damaged air pressure switch is a complex issue and will need the attention of a qualified heating engineer. The engineer will look at the extent of the problem and either fix it or advise you to get a replacement.

Radiofrequency pairing

This is whereby there is a communication breakdown between the thermostat and the boiler. Radiofrequency pairing issues result in an oil boiler operating like it got a mind of its own, firing up and shutting down at will.

The fix

Locate your boiler manual and read the instructions on resetting your thermostat to its default settings. Follow the given instructions, and you will be able to resolve the issue, and your boiler will be up and running in no time.

Radiofrequency crossover

A radio frequency crossover is whereby the operation of one boiler interferes with the operation of another one located nearby. This is usually the case when a neighbour uses the same boiler as you, or their boiler uses the same radio frequency system as you.

If your neighbour’s boiler thermostat is set on the same frequency as your’s, they may end up controlling your boiler as the radio signals may get crossed over. When this happens, your boiler will start following a new pattern and will be switching on and off at times when it isn’t supposed to.

The fix

An easy fix would be to talk with your neighbours and see if one has set their thermostat to the same frequency as you. If there is one, you can refer to your boiler manual to find instructions on switching your boiler’s thermostat to a different frequency. Switching to a different frequency will resolve the issue, and your boiler will start firing up when you have programmed.

A faulty diverter valve

This is usually the case when your boiler is firing up for domestic hot water, yet there is no central heating and vice versa. It is caused by a faulty diverter valve that is stuck on one mode of heating and directs the flow of hot water to either the radiators or the hot taps.

The fix

A faulty diverter valve isn’t an issue you can solve using simple DIY methods. You will, therefore, have to call a heating engineer who will free or replace the stock diverter valve.

A faulty PCB unit

The PCB is the brainhouse of the boiler, overseeing the operation of the various electrical components of the boiler and receiving signals from all the sensors in the boiler. Once the PCB gets a signal that there is a faulty component in the boiler, be it the fan, pump, or NTC thermistor, it will initiate a lockout and display a fault code.

It can be hard to diagnose the problem with a faulty PCB unit as the displayed error code might have nothing to do with the PCB unit itself. Therefore, you should immediately contact a certified heating engineer you suspect your boiler’s PCB is faulty.

The fix

The OFTEC engineer will test your boiler’s PCB using a multi-meter to ascertain that it is getting power. And if it is getting power but is damaged, you will have to replace it or invest in a new boiler as the PCB is usually the most expensive boiler component to replace.

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