"Just a quick email to thank you very much for dealing with our Boiler fault so promptly last Tuesday.

To call you at 8.30 in the morning and to have the problem diagnosed and fixed by 1.30 in the afternoon, including a trip to the other side of the city to collect a part, was exceptional service. The Engineer I saw was incredibly knowledgeable, friendly & helpful and I would have no qualms recommending you to others. 

Thanks very much and have a good Christmas."