Kassieutle

Although 16p doesn't sound like a lot, when you multiply it by several hours, 7 days per week, and a dozen winter weeks later, you'll end up wasting a substantial sum.

Generally you want to pay extra for any repairs that want doing as a part of the service – along with the model new parts and labour cost to put in them.
You’ll pay additional for any new appliances too – such as a new carbon monoxide detector.

To see how simple it's to repressurise a boiler serviceteam have written an entire blogs on this subject; Checking the flame color is a simple process to find out if all is well with combustion.

If the efficiency of your boiler is dropping, it is time to schedule a service to search out and restore any problems.

I typically come across boilers and installations the place a condensate lure or its pipework is leaking.
This is particularly dangerous when it is leaking onto a gas pipe for instance.