10 Questions to Ask Before Hiring a Heating Engineer
Your heating system is the most expensive appliance in your home. The engineer who installs, services, or repairs it must be qualified, experienced, and Gas Safe registered. No exceptions.
Our in-house team of qualified, insured heating engineers covers all of NW London.
Get a Quote1.Are you Gas Safe registered — and can I see your current card?
Gas Safe registration is a legal requirement for all gas work. The card shows the registration categories — confirm the relevant categories cover your work (CENWAT for central heating, CCN1 for domestic boilers).
Yes — here is my Gas Safe card. My ID number is X, and you can verify it at GasSafeRegister.co.uk or by calling 0800 408 5500.
Expired card, reluctance to show it, or not knowing their own Gas Safe registration categories.
2.Are you accredited by the boiler manufacturer?
Worcester Bosch Accredited installers, Vaillant Advance partners, and Baxi Approved installers can extend the manufacturer warranty to 7-12 years. A non-accredited installer typically gives only 2 years.
Yes — I am Worcester Bosch Accredited. Fitting a Worcester boiler with me gives you a 10-year parts and labour warranty rather than the standard 2 years.
No manufacturer accreditation, or dismissing the warranty extension as unimportant.
3.What size boiler do you recommend — and how did you calculate that?
Boiler sizing is not guesswork. An undersized boiler struggles to heat the property; an oversized one short-cycles, wasting energy. A proper heat loss calculation determines the correct size.
I carry out a heat loss calculation based on your property size, insulation levels, and number of radiators. For a property like yours, I recommend X kW output — here is why.
Recommending a boiler size based only on the existing boiler model, or "this size works for most houses like yours".
4.What boiler brand do you recommend — and why that one for my property?
Different boiler brands suit different properties. Combi vs system vs regular; high-flow vs standard; which brands have the best reliability data. An experienced engineer has a reasoned view.
For your property and usage pattern, I recommend [brand] because [specific reasons: reliability, parts availability, warranty]. Here is how it compares to the alternatives.
Only recommending the brand they stock, or unable to explain the choice.
5.Do you carry out a full system flush before installing a new boiler?
Old sludge and debris from the existing system will contaminate a new boiler and void the warranty. A powerflush or magnetic filter installation is essential with any boiler replacement.
Yes — I carry out a powerflush of the existing system before installing the new boiler, and fit a magnetic filter. This is essential for the warranty and longevity.
Skipping the system flush, or treating it as an optional extra.
6.Will you provide a Gas Safe certificate on completion?
All gas work must be certified. A Gas Safe commissioning certificate is issued by a Gas Safe engineer confirming the installation is safe and compliant. Without it, the installation is technically unregistered.
Yes — I register the installation with Gas Safe and you receive a certificate. This is required for your home insurance and any future sale of the property.
Not mentioning certification, or claiming it is unnecessary for the work being done.
7.What is your experience with heating systems in period properties?
Victorian and Edwardian properties often have oversized radiators, single-pipe systems, or gravity-fed systems. These require specific expertise — applying modern zoning to an old system can create pressure and flow problems.
I have worked extensively on Victorian properties in NW London. I understand single-pipe systems, gravity hot water cylinders, and the challenges of balancing old radiator layouts.
No experience with period property heating systems, or proposing to simply replace a complex old system with a combi boiler without assessing whether this is appropriate.
8.Can you advise on smart heating controls — and do you install them?
Smart thermostats (Nest, Hive, Tado) and zone control can reduce heating bills by 15-30%. A good heating engineer designs the system with controls that suit your lifestyle, not just the minimum required by Building Regulations.
Yes — I install and commission Nest, Hive, and Tado. I can also advise on multi-zone control with programmable TRVs. For your property, I would recommend X and here is why.
No knowledge of smart controls, or treating them as luxury add-ons not worth discussing.
9.How do you handle the flue — and what are the options?
Flue positioning affects boiler placement options. Regulations restrict where flues can terminate (distance from windows, doors, and corners). An experienced engineer knows the regulations and will not propose an installation that fails inspection.
The flue options for your property are X and Y. Here is why I recommend X — it meets the regulations and gives you the best boiler position.
Proposing a flue position that violates regulations, or not discussing flue options at all.
10.What is covered under your workmanship guarantee — and for how long?
Separate from the boiler manufacturer warranty, the installation itself should be guaranteed. Leaks, connection failures, and incorrect commissioning should be the engineer's responsibility for a meaningful period.
My installation work is guaranteed for 12 months. Any installation defect — leaks, pressure issues, incorrect commissioning — I will return and fix at no charge.
No workmanship guarantee, or pointing only to the manufacturer warranty.
Skip the research — our team is ready
Every heating engineer at Hampstead On Demand is qualified, insured, and experienced with NW London properties. We do the due diligence so you do not have to.
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