Here’s a story we hear far too often.

A homeowner in London gets three quotes for a new boiler. They pick the cheapest. Six weeks later the boiler is making odd noises, the radiators are lukewarm, and nobody picks up the phone.

The boiler wasn’t the problem. The installation was.

A new boiler is one of the biggest spends you’ll make on your home’s comfort, and in a city like London, where properties are old, cramped and full of surprises, small mistakes get expensive fast. This guide covers the nine most common mistakes people make with boiler installation in London, and how to avoid every one of them.

Mistake 1: Choosing on Price Alone

The cheapest quote is rarely the cheapest outcome.

A low price often means a cheaper boiler, a rushed fit, skipped extras like a system filter, or a subcontractor you’ve never met. When something goes wrong, you pay twice.

What to do instead: compare quotes line by line. Check the boiler make and model, what’s included (flue, controls, filter, certificate, warranty) and who actually turns up on the day.

Mistake 2: Not Checking the Engineer Is Gas Safe Registered

This one is non-negotiable. Anyone carrying out gas boiler installation in London must be on the Gas Safe Register. Gas work done badly can lead to gas leaks, fires and carbon monoxide poisoning.

Quick checklist:

• Ask to see the engineer’s Gas Safe ID card
• Check the back of the card to confirm they’re qualified to work on boilers
• Look them up on the official Gas Safe Register using their licence number

A genuine professional will be happy to show you. If they hesitate, walk away.

Mistake 3: Buying the Wrong Size Boiler

Bigger isn’t better. An oversized boiler wastes gas and cycles on and off constantly. An undersized one struggles to keep a family warm.

The right output depends on your home’s size, insulation, number of radiators and how many bathrooms you have. A proper engineer should calculate this, not guess from the number of bedrooms.

This is why a quick phone quote with no questions is a red flag. Good installers ask about your property first.

Mistake 4: Picking the Wrong Type of Boiler

London homes vary enormously, so one answer doesn’t fit all.

• Combi boiler: heats water on demand with no tank. Great for flats and smaller homes where space matters.
• System boiler: works with a hot water cylinder. Handy for homes with two or more bathrooms.
• Conventional (regular) boiler: needs a tank and cylinder. Often kept in larger or older homes with existing systems.

Switching type can be a smart upgrade, but it changes the pipework and the cost. Ask your installer to explain why they recommend one over another.

Mistake 5: Ignoring the Rest of the Heating System

A shiny new boiler connected to a sludgy, rusty system is like pouring clean water into a dirty bottle.

Older London properties often have decades of build-up in the pipes and radiators. That sludge can cut efficiency and shorten your new boiler’s life.

Ask whether your installer will:

• Test the system and recommend a power flush if needed
• Fit a magnetic system filter to catch debris
• Check the pump, valves and controls

You can read more about these services on AlanCo’s Heating services page.

Mistake 6: Forgetting About Controls and Efficiency

Many people focus on the boiler and forget the thermostat. Modern controls (smart thermostats, room thermostats, thermostatic radiator valves) help you heat only what you need, when you need it.

In England, current rules also mean new gas combi boilers are normally installed alongside extra energy-saving measures, such as better controls. Your installer should explain what applies to your home and include it in the quote, not surprise you with it halfway through.

Mistake 7: Leaving It Until Winter (or Until It Breaks)

Most boilers die in the coldest week of the year. That’s when everyone is calling, engineers are fully booked, and prices and stress both go up.

Smarter approach: if your boiler is around 10 to 15 years old, getting a quote in spring or summer gives you time to compare options calmly.

That said, emergencies happen. If your boiler fails suddenly, choose a company that offers genuine 24/7 help. AlanCo Services provides emergency call-outs with no call-out charge, so you’re not penalised for needing help at midnight.

Mistake 8: Skipping the Paperwork

After installation you should receive:

• A Gas Safety / commissioning record from your engineer
• Your manufacturer warranty details (registered properly, so it’s actually valid)
• The user manual and guidance on your new controls

Keep all of this safe. You’ll need it for warranty claims and when you sell your home. Also fit (or check) a carbon monoxide alarm near the boiler. It’s a cheap safeguard that matters.

Mistake 9: Hiring a Company That Subcontracts Everything

Some firms sell the job, then hand it to whoever is available. You never know who is walking into your home or how experienced they are.

A better sign is a company whose engineers are employed directly. That’s how AlanCo Services works. It’s a family-run London business, started by father and son, where the people who quote the job and the people who fit it are part of the same team.

So, What Does a Good Boiler Installation Actually Look Like?

Here’s the simple version:

1. A proper survey or detailed questions about your home
2. A clear, itemised quote with no hidden extras
3. A recommendation that fits your property (and explains why)
4. A Gas Safe registered engineer who shows ID
5. Careful removal of the old boiler and a tidy installation
6. Full testing, paperwork, warranty registration and a walkthrough of your controls
7. Aftercare, including annual servicing

If your installer ticks all seven, you’re in good hands.

Why London Homeowners Choose Local

London has its own challenges: period properties, tight flats, restricted parking, and in some boroughs, conservation rules that affect where a flue can go.

A local team understands this. AlanCo Services is based in Earls Court and covers boroughs across the city, with dedicated pages for boiler installation in Earls Court, Chelsea, Camden, Wandsworth, Westminster, Croydon and more. According to the company, standard installations can be completed within 48 hours, with a warranty for peace of mind.

Final Thoughts

A good boiler installation is quiet, tidy and forgettable. You switch the heating on and it just works for years.

Avoid these nine mistakes and that’s exactly what you’ll get. If you’d like a straight answer and a clear price from a Gas Safe registered team, AlanCo is ready when you are.

FAQ’S

What is the most common mistake people make with boiler installation in London? Choosing purely on price. The cheapest quote can leave out important items like a system filter, controls or proper paperwork, which costs more later.

How do I know if an installer is Gas Safe registered? Ask to see their Gas Safe ID card and check their licence number on the official Gas Safe Register. Make sure the card lists boilers among the work they can carry out.

Which boiler is best for a London flat? A combi boiler is often the most practical choice for flats because it heats water on demand and needs no storage tank. An engineer should confirm it suits your hot water needs.

How long does gas boiler installation in London take? Many standard replacements are completed in one to two days. Moving the boiler or changing the system type can take longer. AlanCo states that installations can be done within 48 hours.

Do I need a power flush with a new boiler? Not always, but if your system has sludge or cold radiators, a power flush and a magnetic filter can protect the new boiler and keep it efficient.

Should I replace or repair my old boiler? If your boiler is over 10 to 15 years old or keeps breaking down, replacement often makes more sense. For a newer boiler with one fault, repair is usually better. An engineer can advise honestly after an inspection.

Can I get an emergency boiler engineer in London at night? Yes. AlanCo Services offers 24/7 emergency call-outs with no call-out charge.

Don’t Let Your Boiler Choose the Day It Fails

Get clear advice, a transparent quote and a Gas Safe registered engineer who treats your home with respect.

📞 Call 020 7835 0784 💬 Message us on WhatsApp 📝 Request your free boiler installation quote

AlanCo Services. Family-run, London-based, no call-out charge, 24/7.