Combi Boiler Replacement London

A combi boiler heats water on demand, straight from the mains, with no cylinder or loft tank to find space for — which is exactly why it's the most common choice in London's flats, maisonettes and mid-size terraces. Replacing an old combi, or converting from a regular or system boiler to one, is our most requested job.

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The part most homeowners get wrong is sizing: a combi that's too small for the property leaves you with weak hot water when more than one tap runs; one that's oversized costs more than it needs to and can short-cycle. Our survey looks at radiator count, bathroom count and simultaneous hot water demand — see our boiler sizing guide for how that works — before we recommend an output.

If you're converting from a regular or system boiler, the survey also covers what changes: removing the old cylinder and tanks, capping off redundant pipework, and checking your incoming mains flow rate can actually support a combi before we recommend one.

Combi replacements are quoted after the free survey — a straight like-for-like swap is priced differently to a full conversion from a regular or system boiler, so we won't give a figure until we've seen the job.

What you get

Free survey to size the combi correctly for your radiators and bathrooms
Straight swap or full conversion from a regular/system boiler
Mains flow rate checked before a combi is recommended
Old cylinder and loft tank removal quoted as part of a conversion
Fixed price agreed in writing before work starts
Fully Gas Safe registered engineers, Benchmark commissioning completed

How it works

A method, not a guess

Free Survey

We check your radiators, bathrooms, incoming mains flow rate and existing boiler location to size the replacement correctly.

Fixed Quote

A written quote covering the new combi, installation and — if you're converting — removal of the old cylinder and tanks.

Installation & Conversion

Your engineer fits the new combi, makes good any pipework changes, and removes redundant cylinder or tank pipework where relevant.

Commissioning & Handover

The boiler is commissioned to the manufacturer's Benchmark checklist and you're shown how the new controls work.

Questions

Combi Boiler Replacement FAQs for London homeowners

Can I convert from a regular or system boiler to a combi?

Usually yes, provided your incoming mains flow rate can support it — this is one of the things checked in the free survey. Conversion involves removing the old cylinder and tanks and capping redundant pipework, which the quote covers.

Why is my hot water weak with a combi boiler?

The most common cause is an undersized combi for the number of bathrooms or a restricted incoming mains flow rate. If you're replacing an existing combi for this reason, tell the surveying engineer — it changes what output we'd recommend.

Will a combi boiler work with my existing radiators?

In almost all cases, yes — a combi heats the same radiator circuit as any other boiler type. The survey checks radiator count and condition to make sure the output recommended will heat them properly.

How long does a combi-to-combi swap take?

A like-for-like swap in the same location is often a single day. A conversion from a regular or system boiler, including removing a cylinder and tanks, is more commonly one to two days — your quote will state the expected timescale.

Do I lose my airing cupboard space converting to a combi?

You gain it back, typically — removing the hot water cylinder frees up the airing cupboard. Loft tank removal (if present) frees up loft space too. Both are quoted as part of a conversion if you want them removed.

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