Why does my boiler keep turning on and off?

It can be frustrating when things don’t work the way they’re supposed to. Arguably more so than when something breaks altogether. Boilers certainly fall into this category, as they can experience faults that cause them to turn on and off of their own accord. This can lead to the property becoming too hot or cold and more importantly, causing a loss in heating efficiency.  

It’s therefore important to understand why boilers can turn on and off seemingly at random and what can be done to fix it. Continue reading to find out. 

What is boiler short cycling? 

When a boiler turns on and off constantly, it’s known as short cycling. This typically occurs as a result of the boiler’s preheat function. Although frequent starting and restarting only happens when there is a miscommunication between components. 

In short cycling, the internal thermostat of the boiler detects that the water within the system is cooling down and decides to compensate. This cooling occurs naturally when the central heating is turned off. The boiler then heats just enough water so the thermostat can register a higher temperature. After this short time, it turns off and the cycle repeats. 

Short cycling can put strain on the boiler through the process of constantly reheating the water at a rapid pace. In addition, this can lead to an inflation in gas and energy bills. As such, it is a problem that should be addressed as soon as possible. Whether this is through inspection and remedial action or boiler replacement parts, it’s a cheaper alternative than buying and fitting a new boiler. 

Reasons for boiler malfunction 

There are many parts in a boiler that are all working towards monitoring water temperature and providing heat. As such, there can be many internal and external factors affecting the system which could lead to short cycling. Some common reasons include: 

Faulty electronics 

A boiler’s thermostat, timer, and other digital controls serve to dictate how the unit functions. If any of these connections are faulty, it can cause incorrect signals to be sent that trigger certain processes. In the case the thermostat is misinterpreting water temperature levels, it can result in short cycling. 

Issues with water flow 

Water flow is tied closely to boiler performance. As a result, many boilers will have measures in place that cause them to turn off when internal water reaches a certain temperature. Slow flow causes water to heat up more than usual due to increased exposure to the boiler heat exchanger.  

Short cycling can happen due to this, as the boiler will keep overheating and turning off until the problems is fixed. Boiler water flow issues can arise due to limescale, and sludge build up, as well as defective valves. 

Boiler size  

Sometimes a boiler will be too powerful relative to the property it is housed within. This can happen when larger buildings are partitioned, and the original boiler is still used to heat one of the new properties. When boilers are oversized, they are able to satisfy the property’s heating needs much quicker than expected. This results in an overheating effect where the boiler is forced to cycle to maintain a consistent temperature. 

Incorrect setpoint 

All boilers come with internal controls that govern its response to certain conditions. These include the operator, limit, and (sometimes) modulating. How these setpoints relate to each other has a direct effect on the boiler’s overall functionality. If any are formatted incorrectly, they can interfere with one another and potentially cause the boiler to switch on and off. 

A technician can resolve this issue by resetting the boiler to its last functional setpoints. Although, it may also be necessary to have to source some replacement boiler electrical components. 

Quality boiler spare parts UK 

If a boiler is turning on and off in quick succession, it doesn’t mean the entire unit needs to be replaced. The above causes each have relatively straightforward solutions, so long as you can source the right boiler replacement parts. At National Boiler Spares, we have a huge range of boiler spares. Contact us today to arrange next day delivery of your parts or a BSI accredited part refurbishment.