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How do system boilers work? | Boiler with Water Cylinder

system boiler installed with a hot water storage cylinder

System boilers, often referred to as sealed system boilers, are a popular choice for heating and providing warm water to homes. In this article, we’ll delve into how system boilers work, compare them to other boiler types, explore their advantages and disadvantages, and offer some guidance on selecting and installing one for your home.

How does a system boiler work?

A system boiler is a closed heating system that operates by heating water in a central heating system and storing it in a dedicated cylinder, typically located in an airing cupboard. The key components of a system boiler include the boiler itself, an expansion vessel, a circulating pump, a pressure relief valve, and the stored hot water cylinder.

1. Boiler: The heart of the system, the boiler, heats water that is then circulated through the central heating system. It is fueled by gas, oil, or electricity.

2. Expansion Vessel: This vessel maintains a stable pressure within the heating system, preventing excessive pressure buildup when the water heats up.

3. Circulating Pump: The pump circulates the heated water from the boiler through the radiators and back to the boiler, ensuring efficient heat distribution.

4. Pressure Relief Valve: It releases excess pressure to maintain system safety.

5. Hot Water Cylinder: The hot water cylinder stores hot water for domestic use, such as showers and taps. It is typically well-insulated to minimise heat loss.

System boiler vs. Combi boiler

System boiler

Works with a separate storage cylinder

Heats water in the cylinder when the heating is on or when a hot tap is turned on

Can provide a powerful and consistent supply of warm water to multiple taps and showers simultaneously

Good for larger homes with 2-3 bathrooms

May require more space than a combi boiler as it needs a storage cylinder

Combi boiler

Heats water on demand, so there is no need for a cylinder

Compact and space-saving

Provides instant heated water, but the flow rate may be limited if multiple taps and showers are running at the same time

Good for smaller homes with one or two bathrooms

More energy-efficient than system boilers

System boiler vs. Regular boiler

Regular boilers, also known as conventional boilers, are another type to consider when comparing boiler systems.

System boiler

More energy-efficient than regular boilers

Can provide a more powerful and consistent supply of heated water

Good for larger homes with multiple bathrooms

Regular boiler

Less energy-efficient than system boilers

May not be able to provide enough hot water for multiple taps and showers running at the same time

Good for smaller homes with one bathroom

Regular boilers consist of a boiler unit, a cylinder, and a cold water storage tank (usually in the loft). They are suitable for homes with high water demands and multiple bathrooms. However, they require more space for installation, including the cold water feed and expansion tank itself.

system boiler installed by our gas engineer

Which type of boiler is best for you?

The best type of boiler for you will depend on your individual needs and circumstances. If you have a large home with multiple bathrooms, then a system boiler is a good option. If you have a smaller home with one or two bathrooms and are looking for a space-saving solution, then a combi boiler is a good option.

It is important to get advice from a qualified gas engineer before choosing a new boiler. They can assess your needs and recommend the best type of boiler for your home.

System Boilers’ Advantages Over Combi Boilers

System boilers offer several advantages over combi boilers, making them an attractive choice for specific situations:

Easier to Install

System boilers are generally easier and quicker to install compared to regular boilers since they do not require a cold water tank. This can lead to cost savings on installation.

  • Great for Busy Households
  • Excellent Water Pressure
  • A Larger Supply of Hot Water
  • Compatible with Solar Energy

No Cold Feed Water Tank Is Required

Unlike regular boilers, system boilers do not require a cold water storage tank in the loft, saving space and simplifying installation.

Strong Water Pressure

System boilers maintain consistent water pressure, ensuring efficient water flow and a satisfying shower experience.

Fast and Economical

System boilers heat water efficiently, reducing energy consumption and heating costs over time.

System Boiler Disadvantages

While system boilers offer many benefits, they do come with a few disadvantages:

More Space Is Needed Than a Combi Boiler

System boilers require space for the cylinder, making them bulkier than combi boilers. This can be a drawback for homes with limited storage space.

Hot Water Isn’t Instant

Unlike combi boilers that provide instant hot water, system boilers may require a short wait for the cylinder to refill and reheat if it has been depleted.

Busier Times May Require a Little Patience

During times of high hot water demand, such as when multiple people in the household are using hot water simultaneously, there may be a slight reduction in water pressure or temperature. However, this is less of an issue with system boilers compared to regular boilers.

system boilers explained to our customer

How Do System Boilers Heat Radiators?

System boilers heat radiators by circulating hot water through them. The boiler heats the water, and a pump ensures that the hot water is distributed efficiently through the radiators, providing warmth to each room.

How Does a System Boiler Heat Water in the Tank?

A system boiler heats water in the dedicated cylinder using a heat exchanger. The boiler’s heated water is transferred to the cylinder, where it is stored until needed for showers, baths, or taps.

Do System Boilers Run Out of Hot Water?

System boilers provide a continuous supply of hot water, thanks to their cylinder. As long as there is hot water stored in the cylinder, you won’t run out of producing hot water, even during peak usage times. However, if the cylinder is emptied, you may need to wait for it to refill and reheat before having hot water again.

Is a System Boiler Better Than a Heat-Only Boiler?

System boilers are typically more space-efficient and provide hot water on demand through a dedicated cylinder. Heat-only boilers, on the other hand, require additional space for a cold water tank and a third hot water tank and cylinder, but they may be more suitable for homes with high hot water demands.

Cost of Running System VS Combi

The cost of running a system boiler versus a combi boiler depends on various factors, including your heating and hot water usage, the energy efficiency of the boiler, and the fuel type. Here are some considerations to help you understand the cost implications:

1. Running Costs: In terms of running costs, system boilers and combi boilers can be relatively similar if they have similar energy efficiency ratings. Both types of boilers heat water efficiently, so the choice may come down to your hot water usage patterns.

2. Hot Water Demand: If you have an increased demand for hot water, especially if multiple taps or showers are in use simultaneously, a system boiler may be more efficient. Combi boilers heat hot water cylinders on demand and can struggle to provide a consistent flow of hot water to multiple outlets simultaneously.

3. Energy Efficiency: Energy-efficient boilers, regardless of type, can help reduce running costs. Look for boilers with high energy efficiency ratings (usually indicated by an ErP rating) and consider whether they are compatible with renewable energy sources like solar panels.

4. Fuel Type: The cost of running a system boiler or combi boiler also depends on the fuel type (e.g., gas, oil, or electricity) and local energy prices. Compare the cost of your chosen fuel source to make an informed decision.

5. Initial Installation Price: The choice to install a system boiler or a new combi boiler, should also take into account the initial installation costs. Combi boilers tend to be less expensive to install because they don’t require a separate cylinder. However, the overall installation cost can vary based on your specific setup and the existing infrastructure.

6. Existing System: If you already have a regular boiler system and are considering changing to a system boiler, it’s essential to evaluate the overall cost, including installation and any necessary modifications to your heating system.

7. Consultation: To determine which boiler type is more cost-effective for your situation, it’s advisable to consult with a local qualified heating engineer. They can assess your home’s heating and hot water needs, consider your budget, and provide recommendations based on your specific circumstances.

Is a System Boiler Worth It?

Whether a system boiler is worth it depends on your individual needs and preferences.

Ultimately, the decision to install a system boiler should align with your specific requirements and budget.

How Long Does It Take for a System Boiler to Heat Water?

The time it takes for a system boiler to heat water can vary depending on several factors, including the size of the hot water cylinder, the starting temperature of the hot water supply, and the boiler’s capacity. In general, a system boiler can heat water relatively quickly, usually within 20-30 minutes or less for the water in the hot water cylinder to reach the desired temperature. However, this time frame can vary, so it’s essential to refer to the manufacturer’s guidelines for your specific system.

Where Do You Put a System Boiler?

A system boiler is typically installed in a convenient and accessible location within your home, often in a kitchen, utility room, or airing cupboard. The primary considerations for average system boiler’ placement include:

Accessibility: The boiler should be easily accessible for servicing and maintenance by a qualified engineer.

Ventilation: Adequate ventilation should be provided in the installation area to ensure proper combustion and safe operation.

Water Cylinder Location: If you have a separate hot water cylinder, the boiler is typically installed nearby for efficient heat transfer.

Space Availability: The chosen location should have enough space to accommodate the boiler and any required pipework.

Regulations: Installation should comply with local building regulations and safety standards.

system boiler and central heating installation

What cylinder do I need for a system boiler?

Selecting the right cylinder for your system boiler is essential to ensure it meets your hot water demands efficiently. Here’s how to determine the cylinder size you need:

Assess Your Hot Water Demand: To determine the appropriate cylinder size, you should assess your household’s hot water needs. Consider the number of bathrooms, the frequency of hot water usage, and the size of your family.

Calculate Required Capacity: A rough guideline for cylinder sizing is that a 125-150-litre cylinder is suitable for a small household (1-2 people), a 150-210-litre cylinder for a medium-sized household (3-4 people), and a 210-300-litre cylinder for a larger household (5 or more people).

Consider Daily Usage Patterns: Think about your daily hot water usage patterns. Do you often have multiple showers running simultaneously, or do you have long baths? This will impact the cylinder size you need.

Factor in Space: Ensure you have enough space to accommodate the chosen cylinder size. Cylinders are typically installed in airing cupboards or other designated spaces.

Consult a Heating Engineer: To make an accurate assessment of your hot water needs and cylinder size, it’s best to consult with a qualified heating engineer. They can perform a detailed heat loss calculation and recommend the most appropriate cylinder for your specific situation.

How to Run a System Boiler Efficiently:

Efficiently running a system boiler involves some simple practices:

Set the Right Temperature: Ensure your boiler is set to the appropriate temperature for your hot water needs. Lower temperatures can save energy while still providing comfortable hot water.

Use Timers and Thermostats: Use timers and thermostats to schedule heating and hot water cycles. This prevents your boiler from running continuously and maintains a comfortable indoor temperature when needed.

Avoid Overheating: Overheating your home wastes energy. Set the thermostat to the lowest comfortable temperature, and consider wearing warm clothing during colder months.

Regularly Bleed Radiators: If your radiators have trapped air, they won’t heat as efficiently. Regularly bleed your radiators to ensure they are heating evenly.

Insulate Pipes: Insulating hot water pipes can prevent heat loss as the hot water travels from the boiler to the taps and radiators.

Monitor Boiler Pressure: Keep an eye on your boiler’s pressure gauge. If it falls below the recommended range, top it up to ensure efficient operation.

Annual Servicing: As mentioned earlier, schedule annual servicing to keep your system boiler in peak working condition.

Things to Consider When Selecting a System Boiler

When choosing a system boiler for your home, there are a few essential factors to consider:

Hot Water Cylinder Size

Ensure that the hot water cylinder’s capacity matches your household’s hot water demands. A larger cylinder is suitable for larger households with higher hot water usage.

Reliable Engineers

MML Plumbing – Your Trusted Local Boiler Installer

The installation of a system boiler is a task that demands the expertise of a qualified and Gas Safe registered engineer. This ensures that the system boiler is correctly placed, adheres to safety standards, and functions at peak efficiency. Trust us for a reliable and safe installation experience.

Frequently Asked Questions

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