The evenings are drawing in across Surrey and the heating is starting to come on for longer. If you’ve booked your annual check and wondered what happens during a boiler service, the short answer is that a Gas Safe registered engineer inspects the boiler inside and out, cleans what needs cleaning, tests it’s burning gas safely and checks the flue and safety devices. Our boiler service and repairs page explains how we carry it out, and here’s what to expect on the day.
Before the engineer starts
The engineer will usually ask a few questions first. Has the boiler been making any noises? Has the pressure dropped? Any fault codes or lockouts? Mention anything you’ve noticed, even if it seems minor.
They’ll also check the boiler is running so they can see how it behaves before anything is touched.
The visual checks
A good service starts with a look at the whole installation, not just the boiler:
- The boiler is secure on the wall and the casing is intact
- Pipework and connections show no signs of leaks or corrosion
- The flue is properly supported, sealed and terminates in a safe position outside
- There’s adequate ventilation where required
- There are no signs of overheating, scorching or soot
Inside the boiler
With the casing removed, the engineer inspects and cleans the main components. Depending on the boiler, this typically includes:
- The burner and the heat exchanger, checked for deposits and damage
- The fan and the ignition and flame sensing electrodes
- Seals and gaskets on the combustion chamber
- The condensate trap, which is cleaned so it doesn’t block
Any worn parts will be pointed out. Some can be replaced on the day; others may need ordering.
Combustion and gas checks
This is the heart of the service. Using a flue gas analyser, the engineer measures what’s coming out of the flue to confirm the boiler is burning gas cleanly and efficiently. They’ll also check:
- Gas pressure and gas rate at the boiler
- That the flue is clearing waste gases properly
- That the boiler’s safety devices shut it down when they should
If the readings are outside the manufacturer’s limits, the engineer will adjust or repair the boiler, or explain what’s needed.
System checks
The engineer will usually check the wider heating system too:
- System pressure and the expansion vessel
- The pressure relief valve and its discharge pipe
- Controls such as the thermostat and timer
- Signs of sludge, such as dirty water or cold spots on radiators
How long does it take?
Most services take around an hour, sometimes longer if the boiler needs extra cleaning or the engineer finds a fault. Very old boilers, or those that haven’t been serviced for several years, can take more time.
How to prepare
- Clear access to the boiler, including cupboard shelves underneath
- Have the boiler manual and previous service records to hand if you have them
- Make sure the gas and electricity are on
- Keep pets out of the way
- Note any issues you want looked at
What you get afterwards
You should get a record of the service showing what was checked and any work done. Keep it safe, as manufacturers usually ask for proof of annual servicing if you claim on the warranty.
If the engineer finds the boiler unsafe, they’ll explain the risk and, with your permission, turn it off. If the boiler is getting old and the repairs are adding up, they may suggest looking at a new boiler instead.
Servicing ahead of winter in Surrey
Autumn is when most people across Woking, Guildford, Camberley and Farnham remember their boiler. Booking before the first cold snap gives time to sort any repairs before you really need the heating, and catches small faults while they’re still small.
Frequently asked questions
Is a boiler service the same as a gas safety check?
No. A gas safety check confirms an appliance is safe to use. A service goes further, cleaning components and checking performance in detail. For homeowners, a service usually covers the safety checks too. Landlords need a gas safety record each year by law.
Do I need to be home during the service?
Usually yes, or someone over 18 needs to be there to give access. The engineer may also need to discuss findings, show you anything that needs attention and get your agreement before switching off an unsafe appliance. If you can’t be there, let a trusted adult know what to ask.
How often should my boiler be serviced?
Once a year is the standard recommendation from manufacturers and is usually a condition of the warranty. If your boiler is showing signs of trouble, such as lockouts or pressure loss, it’s worth having it looked at sooner rather than waiting for the service date.
Time for your boiler service?
If your boiler’s due its annual check, give us a call on 07557 373 042 or drop us a message and we’ll get you booked in before the cold weather sets in.
