Did you just discover that your boiler is acting on its own?
One thing is certain, this behaviour is causing you concern and could have serious consequences for your boiler’s longevity.
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Your boiler could be starting up by itself for a variety of reasons.
Some of these causes are normal and part of the boiler’s operation, but it may be a good idea to consider checking out the latest new boiler costs along the way, others, however, can be caused by faults in the boiler’s central heating system or hot water supply and should be addressed immediately by a qualified heating engineer.
Here’s a list of common reasons your boiler might be randomly firing up:
Reasons why a boiler will randomly fire up
Spontaneous hot water demand causes the boiler to fire up
You may have noticed that your combi boiler turns on and off frequently, especially in winter. Combi boilers provide hot water on demand, which is unlike traditional boilers.
The boiler will respond to a demand for hot water by bursting into life when someone turns on the hot water tap.
Turning on your thermostat to warm up your home
If the thermostat instructs the boiler to heat water and startup, it will obey immediately. If this is the time your combi boiler fires up, then this is normal.
If your boiler fires up randomly and turns on, you can confirm this by setting your thermostat to the lowest and not using your hot taps for a few minutes.
Your boiler should not turn on itself if there is no hot water demand.
If it continues to fire up randomly, your boiler could be in trouble.
Preheat cycle on a combi boiler
It is not a problem if your boiler only fires up once or twice daily.
The pre-heat cycle is the cyclic firing of your combi boiler and shutting down.
The boiler heats water in the system to the appropriate temperatures during the pre-heat cycle. This ensures that hot water is always available when you turn on your hot tap.
Most of the best combi boilers have this pre-heat setting, so it is one to be aware of.
How to check if your combi boiler has a preheat setting?
Check your owner’s manual to confirm if the boiler is performing a preheat cycle. Some boilers, like the Ideal Logic, have the option to turn it on or off on the front panel.
However, if your boiler is constantly on, for example, six times an hour, and then turns off, this is a sign that the boiler is having problems.
You should not attempt to solve the problem yourself.
Instead, call a Gas Safe registered engineer certified to inspect your boiler and fix any underlying problems.
Frost protection feature – common on modern boilers
Most modern boilers include a frost protection function that prevents pipes from freezing in the coldest winters.
Since heating up is the only way to prevent freezing, your boiler will heat up when temperatures drop, and your pipes are at high risk.
You should always check for a frozen condensate pipe too.
The boiler will be shut down once the cold spell is over. It will then wait for the next cold snap to ignite, hence the random firing of the boiler.
Short cycling – a boiler protecting itself
A Short cycling boiler is a process of turning on and off a boiler in a cyclic fashion to avoid overheating. This prevents heat from being dissipated too quickly. This happens when a boiler generates heat faster than your hot water or central heating system can.
Short cycling can cause a boiler to fire up randomly for the following reasons:
- A boiler that is too large for the property
- Internal boiler pump problems
- Pipes that are too small for the central heating system
- Poor central heating system design
- Residues or blockages are known as radiator sludge
Check your gauge for high water pressure
If the water pressure in your central heating system gets too high, it can damage system components and cause the boiler to shut down.
The boiler will start the pre-heat cycle once the boiler pressure has fallen to the right.
You should check your radiators for high water pressure to reduce the possibility of your boiler starting up randomly.
Check if you have a low boiler pressure gauge.
If you have low boiler pressure, this could also be an issue.
A boiler will not fire up if the pressure is low, but if it rises above the right level, it will start flowing hot water.
It will shut down again if the boiler doesn’t circulate hot water effectively. If this keeps happening, you may need to check your hot water pump, or you may have a damaged heat exchanger.
Both of these will require a Gas Safe engineer.
Location of central heating thermostat
If a room gets too hot quickly…
Your central thermostat acts as an on/off switch for central heating in your home.
If the thermostat senses the interior temperature below the set value, it will instruct the boiler to turn off and provide hot water for central heating.
The internal thermostat will turn off the boiler if the internal temperature exceeds the set value.
If a room is too cold, quickly…
If the thermostat is in a drafty area near a front door, fan, or washing machine, it can be affected by drafts from open doors, operating fans, washing machines, and other moving parts.
A sudden breeze will fool the thermostat if someone opens the front door. The thermostat will tell the boiler to heat the room and turn on the heating.
This will prevent you from having to deal with this problem. You can install your thermostat in the living area or the hallway. It won’t be affected if the temperature drops regularly.
Printed circuit board (PCB) fault
Your boiler could be randomly starting up due to an electrical fault within the PCB unit.
If this is the cause, you may need to consider how much a new boiler costs.
As we all know, the PCB is the heart and brain of your boiler and central heating system.
The PCB coordinates the operation and coordination of all your boiler components to ensure they work together.
The PCB can fail to recognise the timer settings, which could cause the boiler to turn on even though it is set for the opposite.
Faulty PCBs are a serious problem and should not be taken lightly.
You should contact one of your local heating engineers right away.
Why does my boiler fire up randomly? do I need a new boiler?
If your boiler is old, you may need a new boiler installed.
If you think it may be cheaper than continuously calling out a heating engineer and labour costs, then you can get free boiler quotes now in under 20 seconds with one of our recommended installers.
