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ComGas Services UK Ltd
ComGas branded graphic for domestic boiler installation
Boiler Installation & Replacement

Boiler Installation & Replacement

A new boiler is sized to your home's actual heat loss and hot water demand, not swapped like-for-like out of habit. We survey the property, confirm the right boiler type, and install, commission and register it correctly — for homeowners and landlords across Farnham, Guildford, Godalming, Farnborough, Fleet and Camberley.

Request a Boiler Quote Call 01252 214120
New boiler decisions

Repair or replace — how to decide.

Most calls start with a broken boiler, not a decision to buy a new one. Before recommending replacement we look at the age of the boiler, the cost and availability of the part needed, how often it has failed recently, and whether the flue, controls and system around it are still fit for purpose.

A boiler under eight years old with a single failed component is usually worth repairing. A boiler that has failed more than once in a year, uses an obsolete part, or is significantly oversized or undersized for the property, is usually better replaced. We give you that assessment plainly rather than defaulting to either answer.

ComGas Services UK Ltd
Gas Safe · OFTEC · REFCOM F-Gas · CHAS · Constructionline

New boiler installation

The right boiler, sized correctly, installed and commissioned properly.

A new boiler is more than a like-for-like swap. We confirm the right type for your household, calculate the correct output, and complete the installation with the checks and paperwork it actually requires.

Choosing the Right Boiler Type

The three boiler types solve different problems, and picking the wrong one is the most common cause of poor performance after installation.

  • Combi boiler — heats water on demand with no cylinder or tank, suiting smaller homes with one bathroom
  • System boiler — stores hot water at mains pressure via a cylinder, suiting homes with more than one bathroom
  • Regular boiler — retains a cylinder and often a loft tank, usually chosen when replacing an existing regular system
  • Type confirmed against your actual hot water usage rather than assumed from what's already fitted
Find out more

Sizing to Your Home's Heat Loss

Boiler output is sized to the property's heat loss, calculated from its construction and radiators or underfloor circuits — not by matching the kW rating of the boiler being removed.

  • Heat loss calculated from wall, window and roof construction, room sizes and heat emitters
  • Output matched to the calculated result rather than the old boiler's rating
  • Hot water flow rate sized separately against actual bathroom demand
  • Oversizing avoided to prevent short-cycling and reduced component life
Find out more

What a Proper Installation Includes

A proper installation is a defined scope of work, checked and recorded, not just a boiler swapped out for another.

  • Heat loss and hot water demand survey of the property before quoting
  • Flue routed and terminated to current Building Regulations and manufacturer instructions
  • Gas supply pipework and meter capacity checked against the new boiler's input rating
  • System cleansed with a power flush where contamination or sludge is present
  • Controls fitted or upgraded — room thermostat, programmer or smart control as appropriate
Find out more

Commissioning & Compliance

Commissioning and registration are what make the installation legally compliant and the warranty valid if something later goes wrong.

  • Full commissioning and a signed Benchmark checklist logged with the manufacturer
  • Building Control notified through the Gas Safe Register's notification scheme
  • Part L of the Building Regulations satisfied as standard
  • Gas work carried out under Gas Safe registration 629080
Find out more
Close view of a component being fitted inside a Vaillant ecoTEC exclusive gas boiler

Commissioned, registered and recorded at handover

Reliability starts before the new boiler is fitted

System cleanliness and modern controls protect the new boiler's warranty.

Sludge and debris from an old system are one of the most common causes of early failure in a new boiler's heat exchanger. Where the existing system shows signs of contamination — black water, cold spots on radiators, noisy circulation — we power flush the system before connecting the new boiler, and fit a magnetic system filter as standard to protect it going forward.

Modern controls make a measurable difference to running cost and comfort. Weather compensation, load compensation, and boiler-specific smart thermostats all adjust flow temperature and firing pattern to match demand rather than running at a fixed setting. We fit or upgrade controls as part of installation, matched to what the boiler manufacturer supports.

  • Power flush and magnetic system filter fitted where contamination is present
  • Weather compensation, load compensation or smart thermostat controls fitted as appropriate
  • Controls matched to what the boiler manufacturer supports
  • A genuine reliability measure, not an optional extra sold for its own sake
Request a Boiler Quote
Manufacturer accreditation

A Vaillant Advance installer

ComGas installs, commissions and services Vaillant boilers to Vaillant's own requirements, and registers every new Vaillant boiler we fit so the guarantee starts correctly. On eligible models that means a 10-year Vaillant guarantee as standard.

  • 10-year Vaillant guarantee as standard on eligible Vaillant boilers
  • Registered with Vaillant within 30 days of installation
  • Benchmark logbook completed at commissioning
  • Annual service by a Gas Safe registered engineer keeps it valid

The guarantee term depends on the appliance, the system protection Vaillant requires and Vaillant's own guarantee conditions, which include an annual service by a Gas Safe registered engineer. We confirm the guarantee that applies to your installation in writing with your quotation.

Vaillant and the Vaillant logo are trade marks of Vaillant Group, shown here to identify the appliances ComGas installs and services.

Residential project

A recent twin-boiler installation in Farnham.

View all projects
Genuine feedback

What homeowners say about ComGas.

Reviews from real ComGas customers, shown as submitted through Google.

Rated 5.0 out of 5 from 75 Google reviews.

"Really happy with the service! Matt came out to carry out our boiler service and was friendly, professional and did a great job."

Kerryann, Google review, September 2026

"First time we've used this company and it won't be the last. Very professional and efficient in everything they do…"

Ian, Google review, June 2026

"…ended up coming to my place of work and sorting an old heating system that hadn't worked for years in a car showroom & workshop. Great team of guys"

James, Google review, October 2025

Read all our Google reviews

Boiler installation questions

Frequently asked questions.

If you're weighing up whether your current boiler needs replacing at all, the first question below covers how we make that call.

Call 01252 214120
How do I know if I need a new boiler or a repair?

Age, fault history and part availability decide it. A boiler under roughly eight years old with a single fixable fault is usually worth repairing. Frequent breakdowns, an obsolete part, or a boiler clearly mismatched to the property's demand point towards replacement. We assess this honestly during any call-out rather than assuming replacement is the answer.

Can I switch from a regular boiler to a combi?

Often yes, where hot water demand suits it, but it means removing the cylinder and tank and reworking pipework, which adds cost and disruption beyond a straight swap. We assess this at survey stage against your actual hot water usage before recommending a conversion.

Will a bigger boiler heat my house faster or better?

No. An oversized boiler short-cycles — switching on and off more frequently than needed — which wastes energy and shortens component life. Correct sizing from a heat loss calculation gives steadier running and better efficiency than simply choosing a higher kW rating.

Do you register the boiler warranty for me?

Yes. Commissioning includes completing the Benchmark logbook and registering the installation with the manufacturer, which is usually a condition of the extended warranty. We also notify Building Control through the Gas Safe scheme as required.

How long does a boiler installation take?

It depends on the scope — a straightforward like-for-like combi swap is quicker than a conversion between boiler types or a full system clean. We confirm timescale at survey stage once the actual work involved is known.

What happens to the old boiler and system?

We remove and dispose of the old boiler responsibly. If the existing pipework or radiators show contamination, we recommend a power flush and filter as part of the installation to protect the new boiler's warranty and performance.

Is a service plan available after installation?

Ongoing annual servicing is available separately once your new boiler is in — see Boiler Servicing for what that includes and why it matters for warranty validity.

Are you a Vaillant installer, and what guarantee comes with a new boiler?

ComGas is a Vaillant Advance installer, and new Vaillant boilers we install carry a 10-year Vaillant guarantee as standard on eligible models. We register the installation with Vaillant within 30 days of completion and complete the Benchmark logbook. The guarantee then stays valid for as long as the boiler is serviced every year by a Gas Safe registered engineer and the service is recorded. Guarantee length varies by model, and other manufacturers set their own terms.

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Residential boiler and heating care

Need a repair, ongoing care, or just your annual service?

Three straightforward options for domestic gas boilers and heating systems. Every price includes VAT, and parts are charged separately on all three.

Boiler & Heating Repair Visit

£99inc. VAT

For when something has already gone wrong and you want an engineer to look at it.

  • Up to one hour of engineer attendance
  • Diagnosis of a domestic boiler or heating-system fault
  • Repair within the included hour where that is reasonably possible
  • A plain explanation of what has gone wrong
  • Advice on any further work the system needs

Parts, materials and any labour beyond the first hour are charged separately. We explain further chargeable work before going ahead wherever it is practical to do so.

Book a Repair Visit

Recommended

ComGas Heating Care

£11.95per month inc. VAT

12 monthly payments£143.40

Annual servicing and extra heating support in one simple monthly plan.

  • Annual service for one domestic gas boiler
  • Heating System Health Check
  • Boiler and heating controls check
  • Gas safety and combustion checks appropriate to the appliance and service procedure
  • Annual service reminder, so the date is not missed
  • Written boiler service record
  • One included repair visit in each 12-month plan period
  • That repair visit during normal ComGas office hours
  • Up to one hour of engineer attendance and diagnosis within the included visit
  • Repair within that hour where reasonably possible and no additional parts are needed

Parts and additional repair labour are charged separately. Out-of-hours attendance is not included. This is a service and maintenance plan, not breakdown insurance.

Apply for Heating Care

Annual Boiler Service

£109inc. VAT

One-off annual servicing for a single domestic gas boiler.

  • Annual service of one domestic gas boiler
  • Boiler safety checks
  • Combustion checks where appropriate to the appliance
  • Boiler condition inspection
  • Boiler and control operation check
  • Heating System Health Check
  • Written service record

Servicing only. If we find a fault, we explain it and quote for the repair separately.

Book Your £109 Boiler Service

All prices shown include VAT and apply to one domestic gas boiler. Replacement parts and materials are charged separately in every case.

Start a conversation

Considering a new boiler, or unsure if yours can be repaired?

Tell us about the fault or the age of your current boiler and we'll advise honestly on the right route before you commit to anything.

Call our team01252 214120 Email enquiriesinfo@comgas.uk

What happens next

  1. We review your enquiryThe office looks at the details and any photos or documents you have sent.
  2. We get in touchWe contact you by phone or email to talk it through and answer your questions.
  3. Visit, survey or quotationWe arrange the right next step for the job: an engineer visit, a site survey or a written quotation.
Enquiry

Get a boiler quote from photos

Send us a photo of your current boiler, plus the flue and pipework if you can, and answer a few quick questions. We use them to prepare your replacement quotation, and we’ll tell you if we need to visit first.

    Photos of your current set-up. The boiler photo is required; the other two help us quote accurately.

    yes I consent to my data being stored and to receive marketing communications. My data can be stored in accordance with the Privacy Policy

    Can’t take photos right now? Call 01252 214120 or use our standard enquiry form.

    Current accreditations and registrations.

    Gas Safe Registered OFTEC Registered REFCOM F-Gas Certified CHAS Accredited Constructionline Approved
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