System Boiler Replacement London

A system boiler heats your radiators directly but stores hot water in a cylinder, which it can refill and reheat under mains pressure — the reason it's the common recommendation for larger London houses with two or more bathrooms where several people might want hot water at once, something a combi can struggle with.

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Replacing a system boiler is usually more straightforward than converting between types, since the cylinder and pipework are typically already in place. Our free survey checks whether your existing cylinder is still fit for purpose or due for replacement alongside the boiler, and confirms the new boiler's output matches your radiator circuit.

If you're moving to a system boiler from a regular (heat-only) boiler with a header tank in the loft, or from a combi that's struggling with multiple bathrooms, the survey covers that conversion too — including whether an unvented cylinder is a sensible upgrade at the same time.

System boiler replacements are quoted after the free survey — whether your existing cylinder can stay or needs replacing is the single biggest factor in the price, so we check it before quoting rather than assuming.

What you get

Free survey to check your existing cylinder and size the new boiler
Straight system boiler swap, or conversion from regular or combi
Cylinder replacement quoted alongside the boiler if it's due
Suited to homes with two or more bathrooms and simultaneous hot water demand
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 assess your radiator circuit, existing cylinder condition and hot water demand across your bathrooms.

Fixed Quote

A written quote for the new boiler and, if needed, cylinder replacement or upgrade to an unvented system.

Installation

Your engineer fits the new boiler and any cylinder work agreed in the quote, with minimal disruption to your water supply.

Commissioning & Handover

The system is commissioned to the manufacturer's Benchmark checklist and cylinder controls are explained before we leave.

Questions

System Boiler Replacement FAQs for London homeowners

Do I need a new cylinder when I replace a system boiler?

Not always — if your existing cylinder is in good condition and correctly sized for the household, it can often stay. The free survey checks this and the quote will say either way.

System boiler or combi — which is right for my house?

It mainly comes down to how many bathrooms need hot water at the same time. Two or more bathrooms with regular simultaneous use tends to favour a system boiler and cylinder over a combi. See our combi vs. system vs. regular guide for the full comparison.

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

Yes — this removes the loft header tank and its associated pipework, and the boiler pressurises the system directly. The survey covers what's involved and what it adds to the quote.

What's an unvented cylinder and do I need one?

An unvented cylinder delivers mains-pressure hot water to every outlet without a loft tank, closer to combi-style pressure but with cylinder-backed storage. It's worth considering during a system boiler replacement if you don't already have one — we'll flag it as an option in the survey, not push it as a default.

How long does a system boiler replacement take?

A straight boiler swap with the existing cylinder retained is often a single day. Cylinder replacement or a conversion from a regular boiler typically adds a day — your quote will state the expected timescale.

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