At JW McDonald Building Services, we provide professional boiler installation, replacement, and heating system upgrades across South London, South East London, South West London, and the Kent borders.
We’ve built a strong reputation for delivering high-quality workmanship, reliable service, and honest advice. Whether you’re upgrading an outdated system or installing a brand-new boiler as part of a renovation, our experienced engineers will guide you through the best solution for your property.
Boiler installations & upgrades
We install a full range of modern, energy-efficient boilers tailored to your home and heating requirements:
- Combination (combi) boilers
- System boilers with pressurised cylinders
- Heat-only (regular) boilers
- Full central heating system upgrades
Our engineers will assess your property, water pressure, and usage requirements to recommend the most suitable boiler type and output.
Boiler Conversions (Upgrade your system & save money)
Many older properties still use low-pressure systems with water cylinders and cold-water storage tanks. These systems often limit water pressure and overall performance.
- We specialise in boiler conversions, including:
- Converting heat-only systems to combination boilers
- Removing old hot water cylinders and storage tanks
- Upgrading to high-pressure hot water systems
- Reconfiguring pipework for improved efficiency
Upgrading to a modern system can significantly improve water pressure, heating performance, and energy efficiency.
Combi Boiler Installations
Combination boilers are one of the most popular solutions for modern homes. They provide:
- Instant hot water on demand
- High water pressure
- No need for tanks or cylinders
- Space-saving installation
This makes them ideal for flats, smaller homes, and properties where space is limited.
Unvented (Megaflow) Hot water systems
For larger properties or homes with higher hot water demand, we also install unvented hot water cylinders (such as Megaflow systems).
Benefits include:
- Strong, consistent water pressure
- Ability to run multiple bathrooms simultaneously
- Reliable hot water supply for larger households
These systems are ideal where maintaining stored hot water capacity is important.
10-Year Boiler Warranty for Peace of Mind
Our Gas safe engineers are qualified to install leading brands including Vaillant and Glow-worm boilers, offering up to a 10-year manufacturer warranty*. This gives you long-term peace of mind, knowing your boiler is protected and installed to the highest standards.
* annual servicing is required to keep warranty valid
Power Flushing & System Protection
We strongly recommend a power flush when installing a new boiler.
This process removes sludge, debris, and build-up from your heating system, helping to:
- Improve efficiency
- Extend the life of your boiler
- Prevent future breakdowns
We also advise on filters and system protection to maintain long-term performance.
Combine your Boiler installation with a renovation
If you’re planning a bathroom or kitchen renovation, upgrading your boiler or converting your heating system at the same time is often more cost-effective.
This allows us to:
- Upgrade pipework while walls and floors are already opened
- Install new heating systems alongside bathroom or kitchen works
- Reduce overall labour costs and disruption
Many of our clients choose to carry out boiler conversions alongside full refurbishments for maximum efficiency and value.
Our installation process
When installing or replacing a boiler, we carefully plan every stage to ensure safety, compliance, and performance:
- Full assessment of your current system
- Safe isolation of gas, water, and electrical supplies
- Correct sizing of the boiler for your property
- Installation of pipework, flue, and drainage systems
- System flushing and testing
- Final commissioning and safety checks
All installations are carried out by:
- Gas Safe registered engineers
- Qualified heating and plumbing specialists
Boiler size guide (General)
As a rough guide:
| 24kW 1 bedroom flat | 26kW 1–2 bedroom flat |
| 28kW 2–3 bedroom house | 30kW 3–4 bedroom house |
| 35kW 4–5 bedroom house |
We will always confirm the correct sizing based on your property and usage.
Combi vs Heat-only Boilers – Which is right for your home?
Choosing the right type of boiler is an important decision that depends on your property size, water usage, and existing system. The two most common options are combination (combi) boilers and heat-only (regular) boilers.
Combination (Combi) Boilers
Combi boilers provide hot water on demand and do not require a separate hot water cylinder or storage tanks.
Benefits:
- Instant hot water whenever you need it
- High water pressure
- Space-saving (no tanks or cylinders required)
- Energy efficient – only heats water when needed
- Ideal for flats and smaller to medium-sized homes
Things to consider:
- May struggle with multiple bathrooms running at the same time
- Relies on mains water pressure
Heat-only (Regular) Boilers
Heat-only boilers work with a hot water cylinder and cold-water storage tanks, usually located in a loft.
Benefits:
- Better suited for larger homes with multiple bathrooms
- Can supply hot water to several outlets at once
- Works well in properties with lower mains pressure
- Compatible with older heating systems
Things to consider:
- Requires more space (cylinder + tanks)
- Slower hot water recovery compared to combi systems
Which option should you choose?
- Combi boilers are ideal if you want to save space and have a modern, efficient system for a smaller household.
- Heat-only systems are better for larger properties with higher hot water demand.
If you’re unsure, our experienced engineers will assess your current setup and recommend the most suitable option for your home.
We often install combi boilers as part of boiler conversions, removing old cylinders and tanks to create a more efficient, high-pressure system
Areas we cover
We provide boiler installations across:
- South London, South East London, South West London and Kent borders
Including Bromley, Beckenham, Orpington, Petts Wood, Hayes, Shortlands, Biggin Hill, Greenwich, Lewisham, Dulwich, Clapham, Streatham, Wandsworth and surrounding areas.
Guarantees
- 12-month workmanship guarantee
- Manufacturer warranties up to 10 years (selected boilers)
Get a Free Quote
If you need a new boiler, system upgrade, or conversion, contact JW McDonald Building Services today for a free, no-obligation quote.
📞 0800 335 7772 / 07713 741026
📧 info@jwmcdonaldbuildingservices.co.uk
💬📞WhatsApp 07421 203625
Reliable boiler installation specialists covering South London and beyond.