A gas boiler service usually takes between 30 minutes and an hour. An oil boiler service takes a little longer, typically an hour to ninety minutes, because the burner, nozzle and baffles are removed and cleaned. A service that is over in ten minutes is not a service, and one that runs well past two hours usually means the engineer found a fault. Knowing what should happen in that time helps you judge whether you got what you paid for.
This guide walks through a proper service minute by minute, explains the difference between gas and oil, and lists the things that can legitimately make it take longer.
What happens in a gas boiler service
- Visual inspection (5 minutes). The engineer looks at the boiler, its position, the flue, the pipework and the surrounding area for signs of leaks, corrosion, staining or damage, and checks the clearances are still adequate.
- Flue check (5 minutes). The flue terminal outside is inspected, and internal flue joints are checked where accessible. Concealed flues need their inspection hatches opened.
- Casing off and internal inspection (10 to 15 minutes). The front cover comes off. The engineer inspects the burner, heat exchanger, ignition electrodes, seals, fan and condensate trap, and cleans components where the manufacturer’s schedule calls for it.
- Gas pressure and combustion test (10 minutes). The gas working pressure is checked, the boiler is fired and a flue gas analyser measures the combustion readings against the manufacturer’s figures. This is the test that confirms the boiler is burning safely and efficiently.
- Safety devices and controls (5 minutes). Safety cut-outs are tested, the pressure relief valve and expansion vessel are checked on a sealed system, and the controls are confirmed to be working.
- System checks (5 minutes). System pressure is checked and topped up, the magnetic filter is cleaned if fitted, and the engineer asks about any problems you have noticed.
- Paperwork (5 minutes). The service record is completed in the manual or on a service sticker, and a gas safety record is issued if required, for example for a landlord.
What happens in an oil boiler service
An oil boiler service includes everything above plus the parts that make oil different: the burner is removed and cleaned, the nozzle is replaced, the photocell and electrodes are cleaned and set, the baffles are taken out and de-sooted, the heat exchanger is brushed clean, the oil filter is replaced or cleaned, the fuel line is checked for leaks and air, and the tank is inspected. The combustion test is then carried out with the analyser set for oil, checking smoke number as well as efficiency. Our guide to what an oil boiler service includes goes through each item.
What makes a service take longer
- A fault is found. A failing part, a leaking seal or a combustion reading outside the range needs diagnosing and, if the part is in the van, fixing.
- A dirty boiler. A boiler that has missed a few services needs more cleaning, especially on oil.
- Difficult access. A boiler in a tight loft or a boxed-in cupboard takes longer to get at.
- A concealed flue. Opening hatches and inspecting every joint adds time.
- Extra jobs. An unvented cylinder check, a landlord gas safety record covering other appliances, or bleeding and balancing radiators can be added to the visit.
What a too-short service looks like
If the engineer never removes the casing, never uses a flue gas analyser and is gone in fifteen minutes, the boiler has been looked at rather than serviced. Manufacturers’ warranty terms require a proper service to the manufacturer’s schedule, and a visual check will not satisfy them. Ask to see the combustion readings; a good engineer is happy to show them.
How often to service
Once a year for both gas and oil. Annual servicing is a condition of almost every manufacturer warranty, a legal duty for landlords on gas appliances, and the single best way to catch a part before it fails in winter. Our guides on how often a gas boiler should be serviced and how often an oil boiler should be serviced explain the timing.
How DCI Boilers can help
DCI Boilers services gas and oil boilers across Cornwall and Devon with Gas Safe and OFTEC registered engineers who service to the manufacturer’s schedule, test combustion with an analyser every time and show you the readings. Fixed prices, no surprises, and honest advice about anything we find. Book your boiler servicing visit, ideally in late summer before the heating season.
Need help now? Call DCI Boilers on 07888 862 603 or get a free quote.
Frequently asked questions
How long does a combi boiler service take?
Around 30 to 60 minutes for a gas combi, including the combustion test and paperwork.
Do I need to be there for a boiler service?
Someone needs to let the engineer in and ideally be there at the end to hear any findings, but you do not need to watch.
Will the heating be off during the service?
Briefly, while the casing is off. The engineer runs the boiler for the combustion test and leaves it working.
Does a boiler service include the radiators?
Not normally. Bleeding and balancing radiators is a separate job, though many engineers will check system pressure and ask about cold spots.