How to Choose a Plumber: A Practical Checklist

Checking Gas Safe registration properly

Anyone carrying out gas work in the UK, including boiler installations, servicing and repairs, must be Gas Safe registered by law. It is not enough to take a business's word for it, since the Gas Safe Register maintains an official public checker where you can enter an engineer's licence number, or search by business name, to confirm registration is current.

It is also worth asking to see the engineer's Gas Safe ID card when they arrive on site, which shows their licence number and the specific categories of gas work they are qualified to carry out, since registration can cover different types of appliance and installation work.

Insurance and liability

Public liability insurance protects you if something goes wrong during the work, for example accidental damage to your property. It is reasonable to ask any plumber or heating engineer to confirm they hold public liability insurance, particularly for larger jobs such as bathroom refits, boiler installations or anything involving significant work inside the home.

For jobs involving more risk, such as unvented cylinder installations or larger renovation projects, it is worth asking whether the individual engineer holds the specific qualifications required for that type of work, since some installations have additional competency requirements beyond general Gas Safe registration.

Written quotes versus verbal estimates

A written quote should set out what work is being done, the materials involved, and the total cost, ideally broken down enough that you understand what you are paying for. A vague verbal figure given over the phone without seeing the job is far less reliable, since the final cost can shift significantly once the work actually starts.

For anything beyond a very small job, it is reasonable to expect a written quote before work begins, and a good plumber will not be offended by being asked for one. Comparing two or three written quotes for anything substantial, such as a bathroom refit or boiler replacement, is generally worthwhile.

Accreditations and what they actually mean

Schemes such as Which? Trusted Trader and TrustATrader are separate, independently run accreditation schemes, each with their own vetting and approval process, and being listed on one does not automatically mean membership of the other. It is worth understanding that these schemes check different things, such as trading history, insurance and customer feedback, rather than assuming any one badge covers everything.

Gas Safe registration is a legal requirement for gas work specifically and is separate again from these trade accreditation schemes, which are voluntary. A tradesperson can be perfectly competent without holding a particular accreditation, but accreditations do provide an additional layer of external checking worth considering when choosing between several options.

Warning signs worth taking seriously

Be cautious of anyone who cannot provide a Gas Safe number for gas work, refuses to put a quote in writing, or pressures you to decide immediately without time to think it over. Unusually low quotes compared with others you have received can sometimes indicate corners being cut on materials or time.

It is also worth being wary of anyone who turns up unannounced offering to check your boiler or find a fault, a tactic sometimes used to pressure homeowners into unnecessary work. A legitimate plumber or heating engineer will always be happy to be booked in properly and to explain exactly what they are doing and why.

Deposits and payment

It is common for larger jobs involving significant materials, such as a new boiler or a full bathroom suite, to require a deposit to cover the cost of ordering parts. However, a large upfront deposit, particularly a request for full payment before any work has started, especially from a tradesperson you have no history with, is worth questioning.

A reasonable approach is a modest deposit tied to materials being ordered, with the balance paid on completion or in agreed stages for longer projects, and this should be set out clearly in the written quote before work begins.

Questions worth asking before you book

Useful questions include how long the company has been trading, whether the same engineer will carry out the whole job, what happens if unexpected problems are found once work starts, and whether there is a guarantee on the work carried out. It is also fair to ask how call-outs and any follow-up visits are handled if something needs adjusting after the main job is finished.

For households in Harpenden, St Albans and the wider Hertfordshire area, it is also reasonable to ask whether the plumber regularly works locally, since a tradesperson who knows the area often has a better sense of typical property types, such as older Victorian terraces with original drainage or 1930s semis with specific boiler configurations.

What a good quote looks like

A good quote is specific rather than vague, itemising labour, materials and any allowances for unforeseen issues, and it should clearly state what is and is not included. It should also set out a realistic timescale and confirm who will actually be doing the work.

If a quote seems unusually brief, avoids mentioning specific materials or fittings, or has no clear payment structure, it is reasonable to ask for more detail before agreeing to anything, since a clear written quote at the outset is one of the best predictors of a smooth job.

Frequently asked questions

How do I check if a plumber is really Gas Safe registered?

Use the official Gas Safe Register checker, which lets you search by licence number or business name to confirm current registration, rather than relying solely on a claim made on a website or business card.

Is it normal to pay a deposit before work starts?

A modest deposit to cover materials being ordered is common for larger jobs, but a large upfront payment or full payment before work begins, particularly with a new tradesperson, is worth questioning.

Does being a Which? Trusted Trader mean the same as being Gas Safe registered?

No, these are entirely separate schemes. Gas Safe registration is a legal requirement for gas work, while Which? Trusted Trader and similar schemes are voluntary accreditation programmes with their own separate vetting processes.

Should I get more than one quote?

For anything beyond a small job, comparing two or three written quotes is generally worthwhile, as it gives you a clearer sense of typical costs and what is being included.

What should I do if a plumber offers to check my boiler unannounced?

Treat this with caution. Legitimate tradespeople do not typically cold-call offering free checks, and this approach is sometimes used to pressure homeowners into unnecessary work.