Guide 01 · Boiler servicing
What actually happens in a boiler service — and what happens when it is skipped.
An annual service is the cheapest thing you will do to a heating system and the easiest thing to put off. Here is what a proper one involves, what separates it from a fifteen-minute glance, and the questions worth asking whoever you use.
Why bother, honestly
Three reasons, in order of how much they will cost you. Safety first: a gas appliance that is not burning properly, or whose flue has been disturbed, is the one appliance in the house that can harm you without making a sound. Second, warranty: almost every manufacturer's guarantee is conditional on an annual service being carried out and recorded, so a missed year can quietly turn a ten-year warranty into a five-hundred-pound repair bill. Third, running cost: a boiler that is short-cycling, over-gassed, under-gassed or fighting a system full of sludge burns money every day it runs, and nothing on the display will tell you.
There is also the unglamorous fourth reason. A service is the one visit a year where somebody who knows what they are looking at sees the whole system — the pressure that has been dropping, the radiator that is cold at the bottom, the flue that a new extension now runs past. Most expensive heating failures were visible a year earlier.
What a proper service covers
- 01
Paperwork and appliance history first
Make, model, age, when it was last serviced, what has been changed and whether anything has been reported since. A boiler that was condemned as at-risk two years ago and quietly turned back on is a very different visit from a five-year-old combi with a full service history.
- 02
Visual inspection of appliance, flue and ventilation
The appliance and its seals, the flue along its whole visible run and at its termination, the ventilation to the space, and whether anything has been built, boxed or plastered around the boiler since it was fitted — which happens more often than you would think, particularly after a kitchen refit.
- 03
Combustion analysis
A flue gas analyser reads what is actually coming out of the appliance and the readings are compared with what the manufacturer specifies. This is the part that tells you whether the boiler is burning cleanly or slowly poisoning its own heat exchanger — and it is the part that gets skipped on a cheap service.
- 04
Gas rate and working pressure
The gas rate is measured at the meter against the appliance’s stated input, and the working pressure is checked while the boiler is firing. A boiler that is being starved of gas will limp along for years, costing money and shortening its own life, and nothing on the front panel will tell you.
- 05
Safety devices proved, not assumed
Flame supervision, overheat and pressure protection: proved by operation rather than ticked because the boiler happened to light. This is the difference between a service and a look.
- 06
Clean, check and reassemble
Condensate trap cleaned and refilled, the burner and heat exchanger cleaned where the appliance and its condition call for it, seals replaced if they are tired, the case sealed properly and the appliance re-tested afterwards. A case seal that does not seal is a carbon monoxide risk, not a cosmetic detail.
- 07
Controls, pressure and the handover
System pressure set, the controls checked and — if you want — actually explained, because a well-set programmer and sensible thermostat settings save more money in a winter than most efficiency upgrades. Then you are told what was found, what is fine, and what is worth watching.
A service is not a landlord certificate
They get confused constantly, including by letting agents. A landlord gas safety check is a safety inspection of every gas appliance and flue in a property, carried out annually by a Gas Safe registered engineer, and it produces a certificate the tenant must be given. It does not include the cleaning and maintenance work that makes up a service, and it is not a substitute for one. A service is maintenance of a single appliance for the owner's benefit. Most landlords are better off having both done in the same visit — there is a full page on the certificate side.
Landlord gas safety explainedSigns not to sit on between services
- A yellow or lazy flame rather than a crisp blue one on an appliance where you can see it
- Black or sooty marks on or around the casing
- The boiler locking out, or needing repressurising more than occasionally
- Banging, kettling or gurgling that was not there last winter
- Radiators taking much longer to heat, or hot at the top and cold at the bottom
- Condensation on the windows of the room the boiler is in, when that is new
- Any carbon monoxide alarm sounding — in which case ventilate, turn the appliance off and get out
If you can smell gas, do not ring a plumber first. Ring the National Gas Emergency Service on 0800 111 999, turn the supply off at the meter if you can reach it safely, open windows, leave the electrics alone and get everyone out of the building.
Four questions worth asking anyone
“Can I see your Gas Safe card?”
Every Gas Safe registered engineer carries one, with a photograph, an expiry date and the specific appliance types they are signed off for. Checking it is normal and nobody competent minds. You can look any registration up on the Gas Safe Register yourself.
“Will you be using a flue gas analyser?”
If the answer is vague, the service is a look rather than a service. Combustion readings are the only objective measure of how the appliance is actually burning.
“What will you do if you find something wrong?”
You want to hear that you will be told what was found, what class of fault it is, what it takes to put right and what it costs — before anything is done, not after.
“Does this keep my warranty valid?”
A service should be recorded properly — in the benchmark book or on a certificate — because that record is what a manufacturer will ask for in year seven.
Boiler due, or overdue?
Gas work is carried out by Gas Safe registered engineers, and a service can be booked alongside a landlord certificate in the same visit. Ring 01483 235549 or email the office — Mon–Fri, 7.30am–6pm · closed Saturday & Sunday.