Guide 01
Boiler servicing: gas, oil, and what actually happens.
“Boiler service” covers everything from twenty minutes with a screwdriver to a proper strip and clean with instruments on it. This is what the job involves on each fuel, so you can tell which one you have been sold — by anyone, not just by JET Heating.
Why once a year, honestly
There are three reasons, and only one of them is usually mentioned. The first is safety: a gas or oil appliance burning badly in a sealed modern house is the one household risk you cannot see, smell or hear. The second is money — a boiler with a fouled heat exchanger or a badly set combustion head burns more fuel for the same heat, every hour, all winter. The third is paperwork: most manufacturers' warranties require an annual service by a registered engineer, and a warranty claim is refused quickly when there is no service history.
The best time to book is late summer or early autumn. Not because engineers say so, but because a fault found in September is an appointment and a fault found in December is an emergency — and because the boiler has been sitting idle for months, which is exactly when seized pumps and stuck valves reveal themselves.
On a gas boiler
Carried out by a Gas Safe registered engineer. £99 + VAT for the annual service; £150 + VAT where the boiler needs the full strip and clean described below.
- 01
Combustion analysed, not guessed
A flue gas analyser goes in the sampling point and the readings are compared against what the manufacturer specifies. It is the single most informative thing an engineer does, and it is the step most often skipped on a rushed service: the numbers tell you whether the boiler is burning cleanly, running rich, or quietly producing more carbon monoxide than it should.
- 02
Case seals and the flue
A room-sealed boiler is only safe while the case seal is intact and the flue is sound along its whole length, including the part hidden in the ceiling void. Seals get brittle, flue joints get knocked by other trades, and terminals get blocked by nests or rendered over by builders.
- 03
Gas rate and working pressure
The gas rate is measured at the meter and checked against the boiler's input rating, and the working pressure is checked at the appliance while it is firing. A boiler starved of gas, or fed at the wrong pressure, will keep limping along while costing you money and shortening its own life.
- 04
Safety devices actually tested
Flame supervision, overheat protection and the condensate route are all tested rather than glanced at. On a condensing boiler a frozen or badly-run condensate pipe is the most common cause of a lock-out on the coldest morning of the year — and the cheapest thing to put right in advance.
- 05
Controls, pressure and the system around it
A boiler is not the whole heating system. System pressure, the expansion vessel charge, the pump, the zone valves and whether the programmer and thermostat are doing what they claim all get looked at, because most "boiler faults" turn out to live outside the boiler.
Basic service or full strip and clean?
A basic service is the right job for a boiler that has been looked after and serviced in the last couple of years: checks, tests, readings, and a clean where it is needed. A full strip and clean is for the boiler that has not been opened in years, is sooting up, is short-cycling, or has started locking out — the burner and heat exchanger come out, get cleaned properly, go back and are re-tested. If you are not sure which yours is, describe its age and history on the phone and you will get a straight answer rather than the more expensive one by default.
On an oil boiler
Carried out under OFTEC registration — a separate qualification from gas. £149 + VAT. Around Shipbourne, Plaxtol and the Sevenoaks villages this is the more common service of the two.
- 01
Nozzle replaced, every time
An oil nozzle is a precision part that wears. It is replaced at service, not cleaned and refitted — a worn nozzle sprays a poor pattern, which means soot, poor efficiency and a boiler that will not hold its settings.
- 02
Filters, pump and electrodes
Tank and line filters changed, pump pressure checked against specification, and the ignition electrodes cleaned and gapped. Most "the oil boiler will not light" call-outs come back to one of those three.
- 03
Baffles and combustion chamber cleaned
Soot is an insulator. A few millimetres of it on the baffles and in the chamber puts a real dent in efficiency, so it is brushed and vacuumed out rather than left because the case was hard to get off.
- 04
Combustion set up with instruments
Smoke number, CO2 and flue temperature measured and the combustion head adjusted to the manufacturer's figures. An oil boiler set by eye can burn noticeably more oil per year than the same boiler set with an analyser, which is money in a tank you paid for up front.
Ring before the service is due if…
- · the boiler locks out and needs resetting more than occasionally
- · system pressure keeps dropping and you keep topping it up
- · there is yellow or sooty staining anywhere around the case or flue
- · radiators are hot at the top and cold at the bottom
- · the boiler is noisier than it was — banging, kettling or a new hum
- · hot water has gone lukewarm, or runs hot then cold
If you can smell gas, stop
Do not ring a heating engineer first. Ring the National Gas Emergency Service on 0800 111 999 straight away. Turn the gas off at the meter if you can reach it safely, open the windows, do not touch any electrical switches and get everyone out of the house. Ring JET Heating afterwards to put right whatever caused it.
Book a service
Mon–Sat, 8am–6pm · closed Sunday. Gas £99 + VAT, oil £149 + VAT, full strip and clean £150 + VAT.