Upgrading to a new combination boiler is one of the few jobs where getting it wrong is expensive and getting it right pays for itself — call 020 7183 4810 for a fixed-price survey. We’re a Vaillant approved installer, Gas Safe registered, and we fit A-rated combis across Westminster’s period properties and modern homes alike.
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A combi boiler installation touches your gas supply, your water system and your flue all at once, which is exactly why it’s not a job to piece together from guides — it’s a legally regulated installation from start to finish. Here’s what to know before you book one in Westminster.
Signs it’s time for a new combi
- Your current boiler is over 10–12 years old and needs frequent repairs. Parts get harder to source and each repair is a smaller saving against a full replacement.
- Hot water pressure or flow is weak, especially with more than one bathroom in use. An undersized or ageing combi struggles to keep up with modern household demand.
- Energy bills have crept up year on year. Older non-condensing boilers run well below the 92%+ efficiency of a modern A-rated combi.
- You’re converting from a tank-and-cylinder system. Removing loft tanks and airing-cupboard cylinders frees up real space, but it changes your plumbing and gas supply and needs proper design, not a like-for-like swap.
- You’re renovating or extending. A kitchen refit or loft conversion is the natural point to reposition or upsize a boiler correctly.
Why this isn’t a job to take on yourself, or hand to an unregistered fitter
| The shortcut | What actually goes wrong |
|---|---|
| “Get a cheap fitter who isn’t Gas Safe registered” | It’s a criminal offence under the Gas Safety (Installation and Use) Regulations 1998 for anyone unregistered to install a gas boiler, and your home insurance can refuse a claim if something goes wrong afterwards. |
| “Reuse the old gas pipework as-is” | Modern combis often need a larger gas pipe to deliver enough volume at the right pressure. Skipping this check can starve the boiler of gas and cause ignition faults from day one. |
| “Skip the system flush and magnetic filter” | Old sludge and debris left in the radiators will circulate straight into your brand-new boiler and can invalidate the manufacturer warranty within months. |
| “Route the flue wherever’s easiest” | Flue position is governed by strict clearance rules from windows, boundaries and balconies. Get it wrong and building control can require it moved at your expense. |
Stop and call us before you commit to a DIY or unregistered install if…
- You’ve been quoted by someone who can’t show a Gas Safe registration card
- The quote doesn’t include a power flush and magnetic filter
- You’re converting from a tank system and the quote doesn’t mention checking your gas pipe size or mains water pressure
- Nobody has surveyed your property in person before quoting
What it costs to get it wrong
An installation done by someone without Gas Safe registration is not just risky, it can leave you without a working warranty, without insurance cover if something fails, and facing the full cost of redoing the work properly. Skipping a power flush is one of the most common reasons a new boiler fails early — manufacturers can and do refuse warranty claims where BS 7593 flushing wasn’t carried out and documented.
Undersized gas pipework causes ongoing ignition problems that keep coming back until it’s corrected. None of these are things you can see by looking at the finished boiler on the wall.
How Olia’s Plumbing & Heating handles it
- Survey. We assess your hot water demand, mains pressure, gas pipework and the best boiler location in person.
- Fixed quote. One clear price covering the boiler, flush, filter and controls — no surprises.
- Install. Full system drain-down, power flush, magnetic filter, correctly sized pipework and a properly routed flue.
- Commission and certify. Combustion analysis, Gas Safe registration and a completed Benchmark logbook so your warranty is valid from day one.
- Clean finish and handover. We talk you through your new controls before we leave.
- Gas Safe registered, Vaillant approved installer
- Manufacturer warranties up to 12 years, registered on completion
- Fixed price agreed before we start
- Experienced fitting combis into period Westminster properties as well as new builds
- BS 7593 power flush and magnetic filter included as standard
Get a fixed-price quote for your new boiler.
Free home survey across Westminster.
Frequently Asked Questions
How long does a combi boiler installation take?
A straightforward like-for-like combi swap usually takes a day. A conversion from a tank-and-cylinder system typically takes two to three days. Call 020 7183 4810 and we’ll give you an accurate timeline after a survey.
What size combi boiler do I need?
It depends on your bathrooms and hot water demand, not just your property size — that’s exactly what our survey is for, so you don’t end up over- or under-specified.
Will a combi cope with two bathrooms running at once?
A standard combi delivers full pressure to one outlet at a time. If your household regularly runs two bathrooms simultaneously, we can talk you through higher-flow options during the survey.
What warranty comes with a new boiler from you?
Between 7 and 12 years depending on the model, registered properly so the cover is valid from the day we finish. Call 020 7183 4810 to discuss which boiler suits your home.
Do you handle the paperwork and building control side?
Yes — Gas Safe registration, the Benchmark logbook and any building notification are all handled as part of the job.
Book your combi boiler installation in Westminster
Call 020 7183 4810 or request a call-back for a free, fixed-price survey.
Related services: Boiler Installation Westminster · Boiler Swap Westminster · Boiler Repair Westminster · Landlord Gas Inspection Central London
Peyman
CEO & Founder — Gas Safe Registered Engineer
Peyman is the founder of Olia's Plumbing & Heating, a London based team with over 15 years of hands on experience in boiler installation and repair, central heating, gas work and emergency plumbing. He personally oversees jobs across Central and West London and writes these guides to help homeowners understand their heating systems.
- Gas Safe Registered
- 15+ years experience
- Covering all of London
