Can I leave my boiler on continuously?

3 October 2023

A question we are often asked is about whether it’s safe – or wise – to just leave a boiler on continuously. It’s perhaps a little more complicated than it sounds because “on” here can mean two different things.

On the one hand, “on” can mean the boiler is literally boiling water constantly, whether that’s for radiators or a hot water cylinder.

On the other hand, a boiler can be “on” but is constantly switching its function on and off in response to the thermostat or radiator valves. This is what we’d consider a normal state of affairs. It’s the most convenient, and it’s really the type of function boilers are designed for.

There’s perhaps a side issue at play too – would you switch the boiler off if you’re not planning to use it. 

Perhaps you’re going on holiday, or it could be summer when you aren’t using the radiators, and you have an electric shower, dishwasher and kettle, so don’t really need your boiler. It’s probably safe to switch your boiler off when you’re going away, but as long as the thermostat is low and you set the timer to switch off heating water, you can leave it on and only use a small amount of power. 

It’s actually good to have the boiler on as it will occasionally fire up momentarily, and that keeps the moving parts exercised, and makes sure nothing freezes up in the winter. 

Understanding the functioning of a boiler

Boilers supply heat to your home in a straightforward way by heating water and, in turn, providing hot water to radiators across the property. The question here is whether it’s good to leave your boiler on continuously. It has implications on your comfort, energy bills, boiler life and, most importantly, safety, so it’s worth exploring. 

Your needs

Whether you have a combi boiler or conventional boiler, it’s there to provide your home with warmth and hot water as and when you need it. When you consider the days when you had to keep an open fire going with coal or logs, and a hot bath was a luxury to be shared by the whole family, we often forget how lucky we are!

But now we have these convenient appliances in our homes, we should use them to make our lives as comfy and safe as possible. Perhaps you have a medical condition that means you need to stay warm – in such cases, you should probably keep it on all the time. It’s also worth noting that a warm house is less prone to damp, and that can be really problematic, especially for the young, the elderly, and people with breathing issues.

A combi boiler will give you hot water on demand, but even that will need a few minutes to get up to temperature if it has been turned off. 

As for your radiators, it can take a good half hour or more to warm them up, and it’s the same for hot water cylinders. 

While it might be possible to plan your life around your expected need for hot water and heat, for most people it’s a constant need. The good news is that once your cylinder and radiators are up to temperature, you don’t need a huge amount of energy to keep them ticking over.

Impact on energy bills

Now more than ever, responsibly managing energy bills is a common concern among householders. If your boiler is in continual operation, it will undoubtedly consume more fuel, leading to higher energy costs. However, this can vary based on the efficiency of your boiler and the insulation of your home.

An older, less efficient boiler continually in operation will use up more energy to maintain its operation compared to newer, energy-efficient models. If your home is poorly insulated, heat loss will occur, and a continually used boiler will struggle to maintain the desired temperature, resulting in higher energy consumption. So, while keeping your boiler on continuously may result in a warmer home, it may also lead to higher energy bills.

There are measures you can take to keep a lid on your bills, however. The easiest and least impactful is simply to turn your thermostat down by a degree or two. You probably won’t notice the difference, but over the course of a year, the energy savings can really add up. You’ll probably get used to a slightly lower temperature, too.

Impact on boiler lifespan

Generally, boilers are sturdy appliances designed to handle long hours of operation. However, leaving your boiler running continuously will inevitably lead to quicker wear and tear, especially if it’s an older model.

Components such as heat exchangers, valves, pumps and other working parts can be challenged by continuing operation. Regular maintenance becomes crucial to ensure a longer life for your boiler if it is in constant use. It’s recommended to schedule annual boiler checks from a certified engineer to ensure the longevity of the system – in fact, your warranty probably demands it too.

As with all things, the longevity of your boiler is a matter of balance, cost and comfort. If you really need it on all the time, then there really is no alternative. You can help yourself by improving your insulation, such as getting your loft or cavities insulated and installing double or triple glazing. That means your home will retain more of the heat that the boiler is producing, so it will not be fired up for as many hours in the day.

Safety considerations

From a safety perspective, boilers are designed to be safe and to operate for extended periods. Modern boilers include a variety of safety measures like overheat cutoffs, pressure relief valves and lockout features, among others. 

Those features protect the boiler against dangerous situations like extreme pressure build-ups or overheating. Nonetheless, safety first should be your motto – always ensure your boiler is serviced regularly by a certified technician and install a carbon monoxide detector as an extra layer of protection.

The ‘always on’ approach vs. timers

So, should you leave your boiler on all day, or should you rely on timers? There are arguments for both cases, and the decision ultimately depends on your specific needs and circumstances. 

Often, homeowners prefer to use timer settings on their boiler for heating and hot water, which can be customized according to your daily routine. This helps with efficient use of energy, as heat is supplied only when necessary. 

On the other hand, some argue that the “always-on” method provides a more comfortable living environment, especially in colder climes, as the home remains warm all the time. It also helps to prevent cold-related issues like frozen pipes. 

However, with modern condensing boilers, the ‘always-on’ approach might prove more energy efficient. These boilers are designed to work at their best when operating at lower temperatures over longer periods, thus using less fuel than when operating at higher temperatures in short bursts.

Whatever setting you have, your boiler will still control the central heating via the thermostat. A thermostat is basically just a switch that tells the boiler to circulate hot water around the radiators when it’s below the desired temperature, and to stop circulating it when it detects that the desired temperature has been reached. 

It’s not a fine-tuning device like a control on a gas cooker or a TV volume control that you can have high, low or medium. So in all likelihood, even if the boiler is “on” all the time, it’s probably switching between on and off quite regularly. 

Remember that hot water is on a different loop, and isn’t connected to the thermostat. A combi boiler will heat up water whenever a hot tap is turned on, otherwise all the energy is going to the radiators. Conventional boilers are a little different, as they heat up the water in a cylinder, and are more likely to be on a timer. A cylinder can be run off a thermostat, which keeps the water nice and hot (until someone runs a hot, deep bath, anyway), but stops it from overheating or heating unnecessarily.

Other factors to consider

There are other considerations too. For example, if you have a system boiler or conventional boiler, the hot water cylinder’s size and insulation will play a significant part in deciding whether the ‘always-on’ approach is suitable. Also, homes in severe weather conditions might benefit from the constant operation of a boiler. 

Overall, the question of whether or not you can leave your boiler on continuously is complex and depends heavily on various factors personal to your situation. Balancing all the factors detailed above can help you make an informed decision. 

For specific advice tailored to your situation, it’s always best to seek the help of a qualified boiler professional who can guide you based on a thorough inspection of your heating system and household insulation capacities. By considering your particular circumstances, personal needs, and energy efficiency, they can provide the best advice on managing your home heating effectively.