On this page
- What should a boiler service include?
- What does the engineer check before opening the boiler?
- How are the flue and ventilation checked?
- Why does the engineer test the gas pressure?
- What gets checked inside the boiler?
- What paperwork should you get after a service?
- Booking a thorough boiler service in Stoke-on-Trent
- Frequently asked questions
Quick answer
A full boiler service should cover a visual inspection of the boiler and pipework, flue and ventilation checks, gas inlet and working pressure, a combustion test with a flue gas analyser, safety device and control checks, cleaning of the condensate trap, inspection of seals, and a completed service record explaining any faults found.
Key takeaways
- A proper service follows a set order, starting with safety checks before the case comes off.
- Gas pressure and flue gas analysis are measured with instruments, not judged by eye.
- The condensate trap and seals are the parts most often found needing attention.
- You should always get a written record of readings and any faults.
Most homeowners never see inside their boiler, so it is hard to judge whether a service was thorough or rushed. The good news is that a proper service follows a fairly consistent set of checks, whatever the make. This checklist walks through them in the order a Gas Safe registered engineer typically works, so you know what should be happening in your kitchen or airing cupboard.
What should a boiler service include?
A boiler service should include visual checks of the boiler, pipework and flue, a check of ventilation where needed, gas inlet and working pressure readings, combustion analysis with a flue gas analyser, testing of safety devices and controls, cleaning of the condensate trap, inspection of seals and a written record of what was found.
Some items depend on the boiler. A combi has hot water checks that a system boiler does not, and an older open-flued boiler needs different flue tests from a modern room-sealed one. But the core is the same, and if several items below were skipped, it was not a full service.
What does the engineer check before opening the boiler?
The first checks are done with the case still on. The engineer looks at how the boiler is installed, whether it is running, and whether anything outside the boiler itself is a concern. Problems spotted here, such as a damaged flue, can change how the rest of the service goes.
- the boiler's condition, mounting and any signs of water leaks, scorching or soot
- the gas supply pipework to the boiler, and whether it is properly supported
- the condensate pipe route, especially any section running outside
- the pressure gauge reading and the system's general behaviour when running
- any fault history shown on the display
How are the flue and ventilation checked?
The flue carries combustion gases out of your home, so it gets careful attention. The engineer follows the flue from the boiler to the terminal outside, checking joints, supports and clearances from windows, doors and vents. Where the flue runs through a void or loft, access to inspect it matters.
Outside, the terminal should be clear of nests, plants and anything stacked against it, with the correct distance from openings. Ventilation is checked against the installation requirements; this matters most for older open-flued appliances, which draw combustion air from the room. If you have boxed a boiler into a cupboard since it was fitted, mention it.
Why does the engineer test the gas pressure?
The boiler is designed to run at a specific gas pressure. The engineer measures the inlet pressure with the boiler off, then the working pressure with it firing at full rate. A working pressure that drops too far suggests undersized pipework, a restriction or a meter issue, and can cause poor ignition and lockouts.
This is one of the checks most often missed on a rushed service, because it needs a manometer connected to the test point. If you want to see how it is done on a real combi, our engineers wrote up checking inlet and working pressure on a combi service.
What gets checked inside the boiler?
Once the case is off, the engineer inspects and tests the parts that keep combustion safe and the boiler reliable. Each item on the list below has a clear reason behind it, which is why skipping one is not a harmless shortcut.
| Check | What the engineer does | Why it matters |
|---|---|---|
| Combustion analysis | Samples flue gases with a calibrated analyser | Shows whether the boiler is burning safely and efficiently |
| Burner and heat exchanger | Inspects for debris and damage, cleans if needed | Blockages affect combustion and heat transfer |
| Ignition and flame sensing | Checks electrodes, gaps and flame detection | Worn electrodes are a common cause of failed starts |
| Safety devices | Tests flame failure, overheat and pressure safety functions | These shut the boiler down if something goes wrong |
| Condensate trap | Removes, cleans and refills the trap | A blocked trap is a frequent cause of lockouts |
| Seals and gaskets | Inspects the case and combustion chamber seals | Keeps combustion products inside a room-sealed boiler |
| Controls and operation | Runs heating and hot water, checks thermostat and timer | Confirms the boiler responds correctly to demand |
In Stoke-on-Trent's hard water area, the engineer will also look for signs of limescale affecting hot water performance on combi boilers.
What paperwork should you get after a service?
You should get a written record of the service, with the date, the engineer's name and Gas Safe registration number, the combustion readings and gas pressures, and a clear note of any defects found. For boilers with a Benchmark logbook, the service record section should be completed as well.
If anything was classed as unsafe, the engineer should explain it in writing and in person, and tell you what needs to happen next. You can check an engineer's registration and the categories of work they are qualified for on the Gas Safe Register. For more on quizzing your engineer, see our list of questions to ask your boiler service engineer.
Booking a thorough boiler service in Stoke-on-Trent
Every item on this checklist is part of our annual boiler service in Stoke-on-Trent, at the prices set out in our boiler service cost guide. Spring is a good time to book, with the heating season winding down.
We cover the moorland edge of the city too, including boiler service in Biddulph and boiler service in Endon. Call 07896 677083 to arrange a time that suits you.
Frequently asked questions
Should the engineer run the heating and hot water during the service?
Yes. The boiler needs to be running for combustion analysis and working gas pressure readings, and the engineer should test both heating and hot water operation before leaving. On a warm spring day the heating may be turned up briefly to make the boiler fire at full rate.
Does a service include bleeding the radiators?
Not normally. A boiler service focuses on the boiler, its flue and its gas supply. If radiators have cold spots, mention it and the engineer can advise, but bleeding radiators is something most householders can do safely themselves with a radiator key.
Will the engineer check my carbon monoxide alarm?
Many engineers will look at whether you have a CO alarm and where it is, and point out if it is missing or poorly placed. Testing and replacing the alarm is usually the householder's job. Press the test button regularly and replace the alarm when it reaches its expiry date.
Sources and further reading
Gasmaster Plumbing & Heating has served Stoke-on-Trent since 2005. Every article is written by our Gas Safe registered engineers (reg. 220932) from day to day work on boilers, heating and gas appliances across Staffordshire, Cheshire and Derbyshire.
