Plumber’s Guide To Choosing The Right Boiler

Choosing the right boiler is one of the biggest decisions you’ll make for your home. It’s not a job to rush.

At Lazard Plumbing, we fit and service gas boilers across Essex and London every week. Hornchurch terraces, Romford semis, the odd Brentwood period property with an existing heating system older than some of our engineers, we’ve seen it all.

This guide covers boiler type, boiler size, fuel type, and the safety rules that matter, so you can choose the right boiler for your home with confidence.

What Type Of Boiler Do You Need?

There are three main boiler types for UK homes: combi, system, and conventional (regular) boilers. The right one depends on property size, bathroom count, and existing pipework.

• Combi boiler: heats water straight from the mains, no separate hot water cylinder or cold water tank needed. Suits flats and smaller terraces.
• System boiler: stores hot water in a cylinder for stronger, steadier flow. Suits homes with two or more bathrooms.
• Conventional boiler: uses a cold water storage tank plus a hot water cylinder, gravity-fed. Suits older properties that already have that setup.

Essex and London housing is a real mixed bag, and that shapes the choice:

• Victorian terraces and conversions often already have a separate hot water cylinder in an airing cupboard, pointing towards a system or conventional boiler
• New-build flats, especially East London ones with barely room to swing a cat, rarely fit a storage cylinder, so combi wins
• Larger commuter-belt houses in Brentwood or Upminster, often four bedroom homes with a large family, need the stronger flow a system boiler provides

The widely used rule of thumb is roughly 1 to 1.5kW per radiator, adjusted for room size and loft insulation. One bathroom, combi’s usually your answer. More than one bathroom with multiple taps and outlets running at once calls for a system or conventional boiler with its own storage cylinder.

Boiler Installation

Here’s how the three compare for typical Essex and London homes:

Combi, System, And Conventional At A Glance

• Combi boilers run from 24kW to 40kW and deliver hot water on demand, though pressure dips slightly if two taps run at once
• System boilers suit family homes needing consistent pressure across multiple bathrooms, with the cylinder tucked in an airing cupboard
• Conventional boilers work well where a loft tank and cylinder are already in place, though older gravity-fed setups can mean weaker pressure upstairs. Unlike regular boilers, combi and system models tend to deliver more even pressure throughout the house

What Size Boiler Does Your Property Need?

Boiler size refers to kilowatt (kW) output, not physical dimensions. Get it wrong and you’ll feel it: an oversized boiler shortens cycles and wastes energy, while an undersized one can’t produce more heat fast enough, leaving showers running cold.

A rough boiler size calculator for combi models:

• Up to 10 radiators: 24kW to 27kW combi boiler
• 10 to 15 radiators: 28kW to 34kW combi boiler
• 15 to 20 radiators: 32kW to 40kW combi boiler
• Heat only boilers and system boilers run lower, from around 12kW upwards, since the cylinder shares the workload

A typical Essex terrace sits around eight to ten radiators. A larger London conversion or four bedroom house can easily hit 15 or more.

Loft insulation, room sizes, window types, and bathroom count all nudge the final figure, so treat the radiator counts above as a starting point rather than a specification. A proper heat loss survey, which works out how much heat each room loses, is the only way to size a boiler correctly.

How Much Does A New Boiler Cost In London And Essex?

Boiler cost varies by boiler type, brand, and installation complexity, so there’s no single figure that fits every job.

A few things affect installation costs in London and Essex specifically:

• Access: a boiler squeezed into a tight kitchen cupboard takes longer to remove and refit than one in an open utility room
• Pipework: older Essex homes with 1960s or 70s plumbing sometimes need extra work to meet current standards
• Property type: period or listed properties around Brentwood can need extra planning around flue positioning to meet building regulations

Examples of how the job itself changes the scope:

• A straightforward combi-to-combi swap in a London flat with pipework already in good nick
• A system boiler replacement in a Hornchurch semi where the cylinder stays put
• A full conversion from conventional to combi in a Romford terrace, tank and cylinder removed
• Fitting a new boiler in a converted period property in Upminster, with extra flue planning needed

We always give a clear, upfront quote before any work starts, so there are no surprises halfway through.

Which Boiler Brands Are Most Reliable?

Worcester Bosch, Vaillant, Viessmann, and Ideal consistently rank among the UK’s most reliable boiler brands, backed by strong warranties and consistently high marks from independent reviewers.

A few extra points worth knowing:

• Most homes on the gas grid opt for a modern condensing boiler, and an A rated boiler cuts both energy bills and carbon emissions compared with older models
• Rural Essex properties off the gas grid sometimes rely on oil boilers, electric boilers, or liquefied petroleum gas systems instead
• Heat pumps are becoming a more common alternative for households moving away from fossil fuels, sometimes paired with solar panels
• Lazard Plumbing backs every boiler installed by our team with our own 24-month workmanship warranty on top of the manufacturer’s cover, so you’ve got parts and fitting both protected

Why Use A Gas Safe Registered Plumber For Boiler Installation?

Can you install your own boiler in the UK? No. Boiler installation, servicing, and repair must be carried out by gas safe registered engineers by law, full stop.

Gas Safe certification confirms an engineer has been properly assessed to work safely and legally with gas appliances, pipework, and flues. Work carried out without it is illegal, and given the risks around carbon monoxide and gas leaks, it’s not a corner worth cutting.

Every heating engineer on our team holds a valid Gas Safety certificate. We cover:

• Boiler installation and replacement boiler swaps across Hornchurch, Romford, Brentwood, and Upminster
• Annual boiler servicing, including chemical inhibitor flushes and new heating controls
• Priority emergency callouts for Lazard Members if anything goes wrong after install

Our friendly team of Essex plumbers and heating engineers look after your home as if it were their own, whether that’s a brand new system going in or an old one being coaxed back to life.

Ready to get your new boiler sorted properly? Get in touch with Lazard Plumbing for a clear, upfront quote from Gas Safe registered engineers covering Essex and London. Find out more about our boiler installation, boiler service and repairs, and power flushing services.

FAQs

How long does a new boiler last?

Most boilers last 10 to 15 years with regular servicing, which keeps components clean and catches small issues before they become breakdowns.

Do I need planning permission for a new boiler in Essex or London?

Standard boiler replacements rarely need planning permission, but flue placement still has to meet building regulations, particularly in terraced houses and flat conversions.

What size boiler do I need for a 3-bedroom house?

A typical three-bedroom house with up to 10 radiators generally needs a 24kW to 27kW combi boiler, though only a proper heat loss survey can confirm the right size for your home. More than one bathroom can tip you towards a system boiler instead.

Is it worth upgrading from a conventional to a combi boiler?

Upgrading frees up loft and airing cupboard space and removes the cold water tank, which suits homes short on space. It costs more than a like-for-like swap, so weigh the space gained against the bigger job.