First of all let us look at differentiating the above
. A plumber can fix leaky taps, install pipes, design and install bathrooms and more. However as soon as gas is involved you need a qualified gas engineer. A gas engineer will be required to install a gas oven, install gas central heating, install service or repair a boiler and find and fix a suspected gas leak.
A Gas engineer in the UK must be Gas Safe Registered. There is an official website where you can check this. Every Gas Safe registered person has a unique number. This register has replaced CORGI.
Beware as some individuals claim to be on the gas safe register and are not. There is a dedicated phone number, easily found on the internet where you can report a bogus gas man or woman.
If you just need work involved that involves water rather than gas then the plumber can help who needs no formal qualifications.
Whichever one is required check to ensure that the person or the business carried liability insurance. This was if an accident occurs you are covered by their insurance.
Many gas engineers will apply a call out charge. Fortunately some do not. If you have a selection find one who does not apply a call out charge.
Check to see how long they have been in business and how much experience they have. Experience counts for everything. The more experience they have then the more times they will have dealt with a similar problem or type of work.
It is always a good idea to check which areas they cover. If they are working away from their own locality is there a reason why. If tradesmen get a bad name then they tend to work further afield and avoid the areas where they have a bad reputation.
Google places is a good way to check for any user ratings. Not everybody knows who to submit a rating and many members of joe public cannot be bothered to submit one. If there is one or more it can be a very good sign.
Lots of tradesmen will come to your home with a portfolio, which will show examples of work that they have done, and before and after shots. Not really a major indicator of quality if you are having a boiler serviced but still a sign of their professionalism.
The web can be really useful for checking good and bad reviews. Not just Google places as mentioned earlier, but lots of sites are around to check. If you just look up the company name you should find any good or bad news.
When you find a decent gas engineer keep his business card handy as you never know when you might need it in an emergency.