If this happens alongside cold or uneven radiators, it’s often worth stepping back and checking whether the issue is boiler-specific or part of a wider circulation problem. Working through a house-wide cold diagnostic can help pinpoint where the restriction is occurring.
Boiler fires then switches off
When a boiler fires and then switches off after a short time, it’s usually because heat is building up too quickly inside the heat exchanger. If hot water isn’t being carried away fast enough, the boiler reaches its internal temperature limit and shuts down to protect itself. After a short pause, it restarts and repeats the cycle.
Restricted circulation is a common cause. Poorly balanced radiators, partially closed valves, or trapped air can all reduce flow through the system. Instead of distributing heat across the house, the boiler ends up reheating a small volume of water repeatedly.
Boiler flow temperature settings can also play a role. If the flow temperature is set higher than necessary, the boiler reaches its cutoff point much faster. Lowering the flow temperature slightly often allows longer, steadier run times without triggering shutdowns.
Why short cycling increases running costs
When a boiler short cycles, it uses energy inefficiently. Each ignition cycle consumes gas or electricity without delivering proportionate heat to the home. Over time, this can increase running costs even if the boiler appears to be operating normally.
In practical terms, short cycling means the boiler is doing more work than necessary to maintain indoor temperatures. Addressing circulation issues or reducing excessive flow temperatures often improves efficiency, allowing the boiler to run for longer, steadier periods rather than repeatedly starting and stopping.
This is one reason short cycling is often linked to higher energy usage in homes that otherwise appear well insulated or adequately heated.
This behaviour is closely linked to how radiators behave during a heating cycle. If radiators heat up and then cool down unexpectedly, it often points to the same circulation imbalance. That pattern is explained in more detail in this guide on radiators that get hot then go cold.
If short cycling occurs alongside uneven room temperatures, it usually indicates the system needs adjustment rather than replacement. Improving circulation, correcting balance, and reducing unnecessary heat buildup often resolves the issue.
When boiler behaviour starts affecting energy costs
Short cycling doesn’t just affect comfort — it can also influence how much energy a home uses over time. Boilers that start and stop repeatedly tend to run less efficiently than those that operate in longer, steadier cycles.
In some homes, this is purely a setup or circulation issue that can be corrected. In others, especially where the boiler is older or oversized for the property, short cycling can persist even after adjustments.
If running costs seem higher than expected, it can be useful to compare current energy usage and tariffs alongside fixing the heating system itself. Improving circulation reduces waste, but the unit rate you’re paying still plays a role in overall cost.
Understanding both sides — how the system runs and how energy is priced — helps avoid overcorrecting one while ignoring the other.
For a wider explanation of how boiler behaviour, circulation, and heat retention interact in UK homes, this is covered in How to Keep a UK Home Warm for Cheap.