Boiler service in London

The combustion analyser is the part that matters. It reads what the burner is producing and tells us whether the appliance is burning correctly, and it is the check that separates a real service from a visual once-over. Alongside that we check gas working pressure at the appliance, flue integrity at the terminal and along its run, the condition of the case and door seals, the condensate trap, and the heat exchanger for scale or debris.

London is a hard water region, which changes what we look for. Thames Water states plainly that all the water in its region is hard, and their own scale classes 200 to 300 mg/l of calcium carbonate as hard and anything above 300 as very hard. That means limescale on heat exchangers and in cylinders is normal here rather than unusual, and it is the reason an annual service earns its keep more in London than it would in a soft water area.

If you are a landlord, booking the annual service at the same time as the gas safety check saves a second visit and a second call-out. They are different jobs — a CP12 is a safety inspection with a legal duty behind it, a service is maintenance — but they are sensibly done on the same appointment.

Worth knowing: since the 2018 amendment to the gas safety regulations you can have the safety check done up to two months before the current certificate expires and keep the original expiry date. That means the annual cycle does not creep forward a few weeks every year, which it used to.