What Happens on Boiler Installation Day in West London?

Waiting on a new boiler is stressful enough without wondering how much disruption to expect in your home. Here is what happens on a typical installation day with our Gas Safe engineers. It covers the key stages from morning arrival to evening signoff. You know when water and power go off. We also show the corners a rushed budget install too often cuts.

Combi swap versus full system conversion

Not every boiler installation is the same job. It depends on what you already have, your bathroom count, and your water pressure. If you are choosing between systems, read our combi vs system boiler comparison.

A conversion is a bigger job. We remove whole components, not one part. Heating stays off overnight unless we leave a temporary electric heater with you between the two days.

What happens on a typical installation day

Here is what a direct combi swap looks like from arrival to handover.

Morning arrival and floor protection. We arrive within the agreed morning window and walk the job through with you. Heavy-duty floor protection goes down from the front door to the boiler cupboard. Worktops underneath get masked too. We treat your home with care.

Safe isolation and drain-down. We prove the boiler’s fused spur is dead with a voltage indicator before touching it. The rest of your sockets and lighting stay live. We never cut your household power. Gas is isolated at the meter. The heating system drains through the lowest drain-off valves. This is when your mains cold water goes off.

Demounting and the flue check. The old boiler comes off the wall and goes straight out to the van. We check the flue exit falls back towards the boiler at a minimum 3 degree gradient, roughly 52mm per metre. That keeps acidic condensate draining safely inside. The new mounting bracket goes up, checked level with a spirit level. It holds the new boiler solid.

Pipework and the gas line check. Older boilers often ran on a 15mm gas supply. A modern 30kW to 35kW combi needs more gas flow than that pipe can reliably deliver. That causes dynamic pressure drops and nuisance lockouts under full load. Where the existing run is undersized, we upgrade it to 22mm copper back towards the meter. We also fit an Adey MagnaClean magnetic filter to the heating return pipe here, catching circulating magnetite sludge before it reaches the new heat exchanger.

Hanging the boiler and the flue. The new boiler goes onto the bracket. It sits straight and secure. The flue assembly is sealed with silicone joints and weatherproofed on the outside wall. Condensate pipework, usually 21.5mm and upgraded to 32mm if it has to run externally, is routed and insulated against winter freezing.

Water back on and pressure tested. Mains water is restored here. Cold taps and toilets are usable again by early afternoon. We dose a chemical cleanser such as Fernox or Sentinel into the system as part of the BS 7593 cleansing process, refill to 1.5 bar, vent every radiator, and run a static leak test before moving on. We leave no joint untested.

Electrics and gas firing. The fused spur is wired and the wireless digital thermostat is paired to the boiler. Gas is turned back on at the meter. We run a full gas tightness test across the property before firing the boiler for the first time. A dynamic inlet pressure test confirms the gas supply holds at or above 20 millibar while the boiler runs at full output, proving the upgraded pipework delivers what the boiler needs.

Combustion analysis and balancing. A calibrated flue gas analyser checks oxygen, carbon dioxide and carbon monoxide levels at the flue sample point, confirming the combustion ratio sits safely under the legal ceiling. Radiators get balanced at the lockshield valves. Every room gets the heat it needs.

Signoff and handover. We complete the Benchmark commissioning logbook against Gas Safe number 657972 and register your manufacturer warranty. We show you how the controls and pressure gauge work. The old boiler, scrap copper and packaging leave with us for licensed recycling. Nothing is left on the driveway.

Exactly how long will I be without water, power and heating?

Water is off for 3 to 4 hours in the middle of the day. Fill a kettle and a jug beforehand so you can make tea or wash hands easily.

Power is a different story. Your household mains breaker stays on the whole time. Lighting, the kitchen ring main, sockets and Wi-Fi are unaffected. We only isolate the boiler’s own fused spur. That lasts 15 to 30 minutes at most.

Heating and hot water are usually back on and tested before we pack up. That means a warm shower that evening.

What cheap “4-hour box swaps” tend to skip

Some subcontracted installs are advertised as finishing in four hours flat. Getting there usually means cutting corners. Speed comes at a cost. And most of what gets cut, you will not see until later.

• Leaving the old 15mm gas pipe in place. A new 22mm run through cupboards or under flooring takes real time. Skip it, and the new boiler goes short of gas under load. That shows up as ignition lockouts once winter demand hits.
• Skipping the chemical flush. Drain it, refill it, leave. No cleansing to BS 7593 means old magnetite sludge gets pulled straight into the new heat exchanger and pump.
• Leaving off the magnetic filter. It is one part. It costs roughly an hour of extra work. Omitting it is enough to void a manufacturer’s parts and labour warranty.
• Getting the flue fall wrong. A flue with no fall, or one sloping the wrong way, sends acidic condensate down the outside brickwork instead of draining safely inside.
• Skipping the gas pressure and combustion checks. Firing the boiler and seeing heat is not proof it is safe. Skip the pressure test and flue gas analysis, and incomplete combustion can go undetected.

What our £2,499 combi installation package includes

Our fully fitted combi installation package starts from £2,499 and includes a new A-rated condensing combi boiler, a horizontal flue kit, a free wireless digital thermostat, an Adey MagnaClean magnetic system filter, a full BS 7593 chemical system cleanse, a free home survey and a fixed written quote before any work begins, plus our 12-month workmanship guarantee. There are no hidden travel markups across West and North West London. Parking is charged at direct council cost only where a permit is required.

Protecting that installation afterwards matters too. Manufacturers require documented annual servicing to keep a warranty valid, so our Homeowner Plan at £9.99 a month bundles your annual boiler service, a 10% discount on repair labour and priority booking. If your radiators are already uneven or cold at the bottom on an older system you are replacing, pairing the new boiler with thermostatic radiator valve upgrades improves balance and cuts running costs from day one.

Can we install a new boiler the same day it breaks down?

Not usually. If your existing boiler has failed completely, a diagnostic visit comes first. Our standard weekday rate is £120, £160 on a Saturday, £180 for an evening call, or £220 for a Sunday emergency. That confirms whether repair still makes sense or replacement is the better route.

A full installation needs a survey, a written quote and often a specific model ordered in. It is rarely a same-day job from a cold start. What we can usually manage is a temporary fix while we schedule the full install within days. If your heating has stopped completely, our emergency boiler repair team can talk through next steps the same day you call.

Getting ready before installation day

A little preparation keeps the day on schedule. Clear the boiler cupboard the night before. Move anything stored underneath it. Fill a kettle and a jug of water first thing in the morning, since the mains will be off by mid-morning. Keep pets in a separate room while tools and pipework are out. Beyond that, there is nothing else to organise. We bring dust sheets and floor protection for the whole route through your home.

Ready for a boiler installation in West or North West London?

If your boiler is unreliable, leaking or facing an expensive repair bill, we make replacement simple and transparent. Tell us your current boiler’s make, model and rough age, and where it is fitted, and we will arrange a free home survey with a fixed written quote and no obligation.

• WhatsApp us: Book in 60 seconds
• Call our team: 020 8051 2124. Our phone line is answered 24/7 and we will get your details to an engineer promptly.
• Explore packages: boiler installation from £2,499 fully fitted, or protect it afterwards with our Homeowner Plan.

We install new boilers across Acton, Ealing, Fulham, Chiswick and the rest of West and North West London. We are Gas Safe registered (657972). Heating that just works, no drama.

Frequently asked questions

How long does a straightforward combi boiler replacement take?

A combi-to-combi swap on the same wall position takes a single working day. Heating and hot water are normally tested and running again before the engineer leaves in the late afternoon. A full system conversion involving a loft tank and cylinder takes 1.5 to 2 days instead.

Will my mains cold water be turned off all day?

No. Mains cold water is off for around 3 to 4 hours in the middle of the day, while the old pipework is disconnected and the new boiler is connected and refilled. We suggest filling a kettle and a jug beforehand so you are not caught out.

Will I lose electricity or Wi-Fi during the installation?

No. Your household mains breaker stays on throughout, so lighting, sockets and Wi-Fi are unaffected. We only isolate the boiler’s own fused spur for 15 to 30 minutes while wiring the new electrical connections safely.

Will my heating and hot water be working the same day?

Yes, on a standard one-day combi swap. Once the system is refilled, flushed and the boiler commissioned, we confirm heating and hot water are working before we leave, usually mid to late afternoon.

Why do engineers sometimes need to upgrade my gas pipe from 15mm to 22mm?

Modern high-output combi boilers need more gas flow than an older 15mm supply can reliably deliver, which causes pressure drops and nuisance lockouts under full load. Upgrading the run to 22mm copper back to the meter, where needed, prevents this.

What happens to my old boiler and the packaging afterwards?

We take everything away. The old boiler, scrap copper and all packaging leave with us for licensed metal recycling. We vacuum the work area and remove our floor protection before we hand the job back to you.

How much does a boiler installation cost in West London?

Our combi boiler installation package starts from £2,499 fully fitted, confirmed with a free home survey and a fixed written quote before any work begins. See our boiler installation page for full package details.