Booking a new boiler is a big investment, so it’s worth taking an extra ten minutes to ask the right questions before you commit. A reliable Gas Safe engineer will welcome your detailed questions and provide clear, honest answers without any pressure. This helps you feel confident in their skills and ensures the installation meets your home’s needs perfectly. Don’t rush, getting the right information upfront can save you time, money, and hassle down the line.
Checks to make before you book your boiler install
Before you pay a deposit or set a date, make sure the installer has properly assessed your home. This should include a site visit in most cases, not just a quick quote over the phone based on your current boiler.
During that visit, pay attention to how thorough they are. Are they checking radiators, pipework runs, your existing controls and where the flue and condensate will go, or are they simply glancing at the boiler and suggesting a like-for-like swap?
Ask what boiler size they recommend and how they have calculated it
Ask whether they suggest a combi system or regular and their reasoning
Ask how they will protect your home and existing pipework
Ask what flushing, filters and controls are included in the quote
An engineer who can explain their recommendations in plain language, without making you feel rushed, is usually a safer choice for a smooth installation.
Key questions for your Gas Safe engineer
Survey and boiler sizing approach
The right boiler size is not just about the size of your current appliance. Ask the engineer how they are sizing the new boiler. They should talk about heat loss, the number of radiators, bathrooms and how you use hot water, not just your property’s number of bedrooms.
If they recommend a much larger boiler “just in case”, ask what that means for efficiency and running costs. Oversized boilers can short-cycle, waste energy, and wear out sooner.
Combi vs system: getting a clear explanation
Ask the installer to explain the pros and cons of combi, system and regular boilers for your specific home. They should discuss things like hot water flow rates, shower performance, space for a cylinder and how many bathrooms you have.
A clear answer will link their recommendation to your lifestyle. For example, one bathroom and limited cupboard space often suits a combi, while busy households with multiple showers may be better with a system boiler and hot water cylinder.
Home protection and mess control
Boiler work can be messy, but a good installer will plan to look after your home. Ask what dust sheets, floor protection and cleaning they provide. They should also explain how they will protect vulnerable surfaces and manage rubbish removal.
It is also worth asking how they will protect carpets on routes in and out of the working area, especially in terraced homes where the boiler is deep inside the property.
Water quality, filters and controls
Flushing and filters for a longer boiler life
Dirty heating water is a common cause of boiler breakdowns. Ask if a powerflush or chemical flush is included and why they recommend one over the other. In many cases, a well-carry-out chemical flush is sufficient, but older systems can benefit from a more intensive clean.
Ask what type of magnetic filter they will fit on the return pipe and where it will go for easy servicing. Also, check if inhibitor chemicals are included as part of the quote, not a last-minute extra.
Controls, thermostats and smart options
Modern boilers work best with the right controls, so ask what room thermostat or smart controls are included. The installer should talk about load or weather compensation and how this can improve efficiency and comfort.
Make sure the quote clearly states whether they are fitting a wired or wireless thermostat, whether any new wiring is needed, and how they will show you to use the controls during handover.
Condensate, paperwork and aftercare
Condensate routing and freezing risks
Condensing boilers produce waste water that must be drained safely. Ask how the engineer will route the condensate pipe and what they will do to minimise freezing risk in cold weather. Ideally, this pipe should run internally as much as possible or be properly lagged outside.
If your existing pipe has frozen in the past, mention this so they can look at improvements, such as upsizing the external section or altering the route.
Warranty, registration and Benchmark booklet
Your new boiler’s warranty depends on correct installation and paperwork. Ask who registers the warranty, how long it is for, and whether any annual service conditions apply. The installer should complete and leave you with the Benchmark checklist in the back of the boiler manual.
Also, ask for a clear invoice and installation certificate, and check when you can expect them. Good paperwork makes future servicing, selling your home or making a warranty claim much easier.
Post installation support and servicing
Before you commit, ask what happens if something is not quite right after the job. Do they offer a workmanship guarantee period, and how quickly do they aim to respond to snagging issues? It is also sensible to discuss future servicing and whether they can carry out your annual boiler service.
You might find it useful to read more about ongoing care in a dedicated boiler servicing guide, so you know what to expect each year.
Local housing points to think about
In many local flats and newer homes, boilers are fitted in tight kitchen or hallway cupboards. Ask your installer how much space they need for maintenance clearances, filters and controls so you avoid cramped, awkward setups. In older terraces, radiators and pipework can be decades old, so discuss any upgrades or pipe alterations needed to suit a modern condensing boiler and protect it from sludge in long, narrow circuits.
Red flags when choosing a boiler installer
A few warning signs are worth taking seriously. Be cautious of anyone offering a full installation quote without seeing the property in person or via a detailed video call with measurements and photos, especially if significant flue or pipework changes are needed.
If the paperwork is vague, for example, “new boiler fitted” with no model, controls, flushing detail or warranty information, ask for a clearer written quote. Walk away from anyone unwilling to show their Gas Safe ID card, explain their registration categories, or let you check them on the Gas Safe Register.
Step-by-step overview of installation day
Arrival, checks and isolation
On the day, your engineer should start by confirming the agreed work, checking access and walking you through the plan. They will identify where to protect floors and surfaces before isolating the gas, water and electricity supplies to the boiler area.
Gas tests are normally carried out before starting any work to ensure the existing installation is safe. This is also the stage where they will confirm the flue position and condensate route with you.
Removal and pipework adjustments
The old boiler and associated parts are then removed, including any redundant fittings or controls. Expect some unavoidable noise as brackets are taken down and pipes are altered.
Your installer will modify or renew pipework to suit the new boiler’s connections and any layout changes agreed, such as moving the boiler or upsizing gas pipework. This can involve cutting floors or lifting boards where necessary, which should be discussed with you in advance.
Fitting, flushing and commissioning
Once the new boiler is fixed in place and connected, the system will be filled and flushed using the agreed method. A magnetic filter and any new controls are installed at this stage, along with inhibitor chemicals.
The engineer will then commission the boiler, running manufacturer checks, measuring gas pressures and combustion, and recording results in the Benchmark booklet. This is also when they set up the boiler’s parameters and control settings for your specific system.
Handover and next steps
At the end, your installer should show you how to operate the boiler and controls, how to top up system pressure if needed, and what to do if you see common fault codes. They should leave manuals, Benchmark documents and a clear record of the work carried out.
You can ask them to point you towards helpful resources, too, such as a guide on gas services in your area, an article on what happens during an installation, or a piece about boiler sizing so you can better understand the decisions made.
Ready to plan your new boiler?
Using this checklist should help you feel more confident before you commit to a new boiler and choose a Gas Safe engineer you can trust. If you are in Gravesend, Medway or Dartford and want clear, honest advice, it can make sense to speak to a local specialist who understands typical homes in the area.
To talk through your options, ask questions from this checklist or book a home survey, contact BCU Plumbing on 08002461041 or visit their gas services and boiler installation page for more details.
