The Ingenious Combi Boiler

The Combi Boiler an Introduction

Combi boilers, short for combination boilers, have become an extremely popular option for domestic heating and hot water in UK homes. This comprehensive guide covers everything you need to know about combi boilers – how they work, types, top brands, costs, installation, efficiency benefits, maintenance, common issues, and more.

What is a Combi Boiler?

A combi boiler, or combination boiler, provides central heating and hot water in a single, compact unit. Unlike a conventional boiler, combis don’t require bulky hot water cylinders or tanks.

Combi boilers are able to heat water directly from the mains supply as it flows through the unit. This gives you hot water on demand rather than having to wait for a tank to heat up. Combis don’t heat water that sits unused in a tank so they are very efficient.

Their compact size and on-demand performance makes combis ideal for smaller homes. By eliminating hot water storage tanks, they save considerable space compared to traditional heating systems.

How Do Combi Boilers Work?

Combi boilers provide central heating and hot water using two heat exchangers inside a single unit. Here is a simple overview of how they work:

• When you turn on a hot tap, a flow sensor tells the boiler to fire up.
• Mains cold water enters the first heat exchanger. This is rapidly heated before arriving at taps.
• For central heating, a thermostat calls for heat. A pump circulates water via a second heat exchanger which warms radiators.
• The boiler uses a gas burner or electric heating elements to heat the water flowing through the heat exchangers.
• Hot water and heating is delivered on demand without the need for storage tanks.

Modern combis are highly responsive thanks to efficient heat exchangers and smart controls. Hot water typically reaches temperature within 5-10 seconds.

Types of Combi Boilers

There are several configurations and fuel types when choosing a new combi boiler:

Fuel Type

• Gas combi boilers – Natural gas models are the most common. They heat water using a gas burner.
• Oil combi boilers – For properties not connected to the gas network. The boiler burns heating oil.
• Electric combi boilers – Heat water using electric heating elements. Good option for properties with cheap off-peak electricity.
• LPG combi boilers – For properties using LPG gas tanks instead of mains gas.

Heat Exchanger Type

• Aluminium heat exchanger – Lightweight but corrosion prone. Needs replacing more frequently.
• Copper heat exchanger – Excellent heat conduction but higher cost. Very long lifespan.
• Stainless steel heat exchanger – Compromise between cost and performance. Most common modern choice.

Condensing vs Non-Condensing

• Condensing boilers – Recover waste heat from flue gases, making them very efficient – over 90% efficiency.
• Non-condensing boilers – Traditional less efficient design with no heat recovery. Only suitable for replacement in unsuitable properties.

Mounting Position

• Wall-mounted combis – Hung on a wall bracket. Most common and versatile combi type.
• Floor-standing combis – Larger and less common. Take up more floor space but easier to service.

Why Choose a Combi Boiler?

There are several key reasons to choose a combi boiler:

Endless hot water – Combis provide hot water on demand, perfect for busy homes where people shower at different times. No more running out of hot water.

Space saving – With no hot water tank needed, combis take up far less room. Great for smaller properties.

Lower energy bills – Their on-demand operation makes combis up to 30% more efficient than traditional heating and hot water systems.

Faster heating – Hot water arrives in seconds. No firing up a boiler and waiting for slow hot water tanks.

Installation simplicity – Less pipework makes combi installation faster and neater. Many can fit onto existing pipework.

For modern homes and lifestyles, a combi makes sense for convenience and efficiency.

Combi Boiler Efficiency and Energy Savings

One of the key benefits of a combi boiler is improved efficiency and energy savings compared to traditional heating systems. There are several reasons why combis can cut your energy usage and bills:

• On-demand hot water – Combis eliminate tank standby losses where stored water gradually cools. Water is freshly heated as you use it.
• Faster heat up – Smaller water volumes heat up rapidly compared to large tanks and cylinders.
• Condensing technology – Modern condensing boilers recover waste heat from flue gases for over 90% efficiency.
• Compact size – With less surface area for heat loss, combis typically retain more heat than bulky tanks.
• Smart controls – Weather compensation and load-sensing features on modern combis adjust fuel and water use intelligently.

By switching from an older non-condensing boiler and tanks to a new combi, models like the Worcester Bosch Greenstar 8000 Life can save a typical household up to £310 per year on energy bills.

Top Combi Boiler Brands

In the UK, the main combi boiler brands include:

• Worcester Bosch – Part of the Bosch group. Market leader in quality and reliability. Eg. Greenstar range.
• Vaillant – German engineering. Premium models with highWhich? scores. Eg. EcoTec range.
• Baxi – Spain’s biggest boiler maker. Reliable mid-range brand popular with installers. Eg. Platinum+ combis.
• Ideal – British brand with innovative features like auto-calibration. Eg. Vogue and Logic+ models.
• Viessmann – Leading German innovation in heating. Renowned build quality. Eg. Vitodens series.
• Glow-worm – Budget UK brand owned by Vaillant. Basic models for value pricing. Eg. Energy combis.

These brands offer combi models to suit all budgets and needs, from value entry-level to premium high-spec boilers.

Combi Boiler Costs

Combi boiler pricing depends on the brand, model, size and features. Typical combi boiler costs:

• Combi boiler price – Entry models from around £500. Mid-range from £600-£900. High-end from £1,000-£1,500.
• Installation cost – Budget around £500-£1,000 for professional combi boiler installation including labour and parts.
• Annual service – To keep your combi in top condition, budget around £80-£120 for an annual service by an engineer.

Additional costs may apply for upgrades like system flushes, thermostats, radiator adjustments and luxury controllers. But overall, combis provide great value for money given their efficiency benefits and longevity of 10-15 years.

Choosing the Best Combi Boiler

Choosing the best combi boiler depends on your budget, property size, hot water demand and preferences:

• Budget – Entry-level combis under £700 suit tighter budgets. Premium models provide extra performance and features.
• Property size – Check boiler kW output meets your heating and hot water needs. Larger homes need higher power ratings.
• Hot water use – Homes with multiple bathrooms or high demand should choose combis with a strong flow rate litres per minute.
• Controls – Consider smart thermostats or internet-connected models for smarter heating management.
• Warranties – Opt for longer warranties from quality brands to cover repair costs. Eg. up to 10 years from Worcester.

An installer can assess your requirements and recommend the ideal combi boiler model to best meet your needs.

Getting Your Combi Boiler Installed

Combi boiler installation involves connecting up the boiler, testing the system for safety, and commissioning the unit. Here’s what’s involved:

• The installer will survey your property to plan suitable locations for the new combi boiler and any associated components like thermostats.
• Most modern combis can fit directly onto existing pipework. Additional valves or adapters may be needed.
• Once piped up, the system is thoroughly flushed to remove debris and tested for gas leaks. A pressure test confirms water-tightness.
• The installer will commission the boiler to optimise settings like heat output, hot water flow rates and weather compensation.
• User manuals and warranties are provided, and the installer explains operation, settings and maintenance needs.
• A Gas Safe registered engineer must perform the installation and provide a safety certificate before use.

Opting for a combi boiler installation package from a brand like Worcester Bosch ensures guaranteed quality installation by accredited installers.

Annual Combi Boiler Service

An annual combi boiler service by a qualified engineer is recommended to keep your system running safely and efficiently. A typical combi service includes:

• Full inspection for faults like corrosion, leaks, or broken components.
• Flushing the heat exchanger to remove limescale buildup.
• Checking gas pressure and combustion performance for optimal efficiency.
• Testing safety devices like the flue, expansion vessel and ventilation.
• Updating the service record and warning of potential issues.

Many manufacturers like Worcester Bosch offer fixed price combi servicing for around £80-£120 per year. This small annual cost helps prevent expensive breakdowns and maintains efficiency.

Common Combi Boiler Problems

While generally reliable, combis can encounter issues needing attention. Common combi boiler problems include:

No hot water – Commonly caused by faulty diverter valves. Try rebooting the boiler and check the valve body for cracks.

Knocking noises – Knocks and banging indicate potential boiler or pump blockages from debris. Requires a flush.

Low water pressure – Pressures below 1 bar suggest a leak. Top up pressure and inspect connections for pinhole leaks.

Erratic hot water flow – Weak flow suggests a blocked heat exchanger or faulty pump. Cleaning and servicing can often resolve flow problems.

Fault codes – Refer to the boiler manual. Simple faults may be resolved by rebooting. More complex issues need professional diagnosis.

Pilot light failures – If the gas burner fails to ignite, check gas supply and listen for sparking. Sensor issues may require an engineer callout.

While worrying, most combi boiler issues can be easily resolved with basic maintenance. An annual service helps spot problems early.

Replacing a Combi Boiler Nearing End of Life

Modern combi boilers have a lifespan of 10-15 years if properly maintained. But eventually, an aging combi will near the end of its working life. Signs include:

• Regular breakdowns and faults developing.
• Unreliable heating and hot water provision.
• Higher running costs as efficiency deteriorates.
• Expensive ongoing repairs due to worn components.
• Difficulty finding replacement parts due to the model being discontinued.

Once your combi boiler exceeds 10 years, it’s advisable to consider replacement. Continuing to patch up an aging boiler can become false economy due to poor efficiency and pricy callout fees over time.

Instead, replacing the combi with an efficient new model will provide reliable service for years to come alongside energy savings from improved performance. Modern innovations also give greater control over your heating.

Combi Boiler vs Conventional Boiler

Combi boilers offer key benefits compared to conventional heating systems:

Hot water

• Combi – On-demand hot water with no tank. Unlimited supply.
• Conventional boiler – Limited hot water tank capacity means possible shortages.

Heating

• Combi – Fast heating activation when thermostat calls for heat.
• Conventional – Slower ignition of boiler needed to heat rads via tank system.

Fuel efficiency

• Combi – Up to 30% more efficient due to on-demand operation without tank losses.
• Conventional – Waste from constantly reheating large stored water volumes in tank and rads.

Space requirements

• Combi – Compact unit with no tanks. Frees up space.
• Conventional – Bulky boiler, water tanks and cylinders take up considerable space.

For modern homes, combis make sense. But continuity of hot water supply may still suit large households with high simultaneous demand.

Pros and Cons of Combi Boilers

Pros	Cons
Provides endless hot water on demand	Flow rates may be weaker on budget models for high demand homes
Heats water and homes rapidly with no wait compared to tanks	Lack of hot water tank provides no backup if boiler breaks down
Compact size saves considerable space	Limited ability to supply multiple taps simultaneously
More efficient than traditional boilers by up to 30%	Less suitable for homes with high, simultaneous demand from multiple bathrooms
Easier and cheaper to install than traditional systems	Requires strong mains water pressure for best performance
Modern features like weather compensation for efficiency	Need more frequent servicing than boilers with separate hot water tanks

Overall, for most homes combis provide the best combination of convenience, space-saving, efficiency, and low operating costs.

Case Study: Upgrading to a Worcester Bosch Combi Boiler

The Wilsons had an 18-year-old non-condensing boiler with a hot water cylinder in their three-bedroom home. Despite annual servicing, the aging system was proving inefficient, unreliable, and expensive to fix.

Their plumber quoted over £300 to replace the broken circulating pump and warned additional issues would likely follow due to the boiler’s age. He recommended replacing the entire system with a modern combi boiler.

Mr and Mrs Wilson chose the Worcester Bosch 30i combi boiler which has a compact size suitable for their kitchen cupboards. The Greenstar model has an A-rating for efficiency and comes with a 10 year parts and labour warranty for peace of mind.

The 30kW output met their home’s heating and hot water needs. Their engineer safely installed the new combi boiler in one day onto the existing pipework after a powerflush.

The upfront investment of £2,200 for the new boiler and installation has already paid dividends through more convenient hot water, lower noise, and reduced annual gas bills by £260 thanks to the 92% efficiency rating. The Wilsons are delighted with their new Worcester Bosch combi boiler.

Conclusion

Combi boilers have become incredibly popular in UK homes due to their convenience, efficiency, space-saving, and cost benefits compared to traditional heating systems.

With rapid hot water delivery, compact dimensions, and innovations like weather compensation – combis make an ideal choice for modern living. By selecting a market-leading brand and ensuring proper maintenance, homeowners can enjoy reliability and energy savings for over a decade.