Guide 01
Boiler servicing, and what actually happens.
“Boiler service” covers everything from twenty minutes with a screwdriver to a proper strip, clean and set-up with instruments on it. This is what the job involves, so you can tell which one you have been sold — by anyone, not just by us.
Why once a year, honestly
There are three reasons, and only one of them is usually mentioned. The first is safety: a gas 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 burns more gas for the same heat, every hour, all winter. The third is paperwork: nearly every manufacturer's guarantee, including the long Worcester ones, requires an annual service by a registered engineer, and a claim in year eight is refused very quickly when there is no service history to show.
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 the same fault in December is an emergency — and because the boiler has been sitting idle for months, which is exactly when seized pumps and stuck zone valves reveal themselves.
What a proper service covers
Carried out by a Gas Safe registered engineer. Ask to see the ID card before work starts — it lists the specific appliances that engineer is signed off for, and the number can be checked on the Gas Safe Register website.
- 01
Combustion analysed, not guessed
A flue gas analyser goes into the sampling point and the readings are compared with 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 twenty-minute visit: 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, along the whole length
A room-sealed boiler is only safe while the case seal is intact and the flue is sound from the appliance to the terminal — including the part buried in a ceiling void or running through a garage roof. Seals go 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, measured
The gas rate is taken at the meter and checked against the appliance’s input rating, and the working pressure is checked at the boiler while it is firing. A boiler starved of gas, or fed at the wrong pressure, limps along costing you money and shortening its own life — and on a long run of undersized pipework that is a surprisingly common finding.
- 04
Safety devices actually tested
Flame supervision, overheat protection and the condensate route are 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 one of the cheapest things to put right in advance.
- 05
The system around the boiler
A boiler is not the whole heating system. System pressure, the expansion vessel charge, the pump, the zone valves, the magnetic filter 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.
- 06
Flow temperature set where it belongs
A condensing boiler only condenses — and only reaches its advertised efficiency — when the water returning to it is cool enough. Left on a factory default of 75 or 80°C it runs hot, short-cycles and never condenses. Dropping the flow temperature to around 55°C and balancing the radiators costs nothing but attention. In the photograph on this site, the display reads 55.0 for exactly that reason.
A service is not a power flush
They get confused often, and they are different jobs. A service is about the appliance: combustion, safety, seals and settings. A power flush is about the water in the pipework — a forced clean to lift out the magnetite sludge that makes radiators cold at the bottom and boilers kettle. A service will tell you whether you need a flush; it will not do one. If a new boiler is going onto old pipework, expect the system to be cleaned, dosed with inhibitor and fitted with a magnetic filter first: most manufacturers require it, and a guarantee claim can turn on it.
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 us afterwards to put right whatever caused it.
Book a service
Mon–Sat, 8am–5pm · Sunday 8am–12pm. Ring either engineer — there is nothing to fill in first.