If your home is off the gas grid, your boiler almost certainly runs on kerosene. Across our area that usually means the rural edges: South Lanarkshire around Lanark, Biggar, Strathaven and the Clyde Valley, the Campsie fringe of East Dunbartonshire, and the hill country of Renfrewshire and East Renfrewshire.
Oil boilers are tough, but less forgiving of neglect than gas. A pressure-jet burner relies on a tiny nozzle, clean oil and correctly set combustion. When any of those drift, sooting, lockouts and bigger oil bills follow.
This guide covers what a proper annual oil boiler service involves, what OFTEC registration means, the Scottish rules on domestic oil tanks, and what to do when the lockout light comes on.
The short answer
- Get an oil boiler serviced at least once a year. OFTEC, Grant and Worcester Bosch all recommend it, and it is usually a condition of the manufacturer's guarantee.
- A full service is hands-on: burner stripped and cleaned, new nozzle, oil filter changed, heat exchanger and baffles cleaned, and combustion set with a flue gas analyser.
- The tank, fire valve and oil line should be checked at the same visit, and you should receive an OFTEC CD/11 servicing report.
- In Scotland, a house tank of 2,500 litres or less needs a bund only where site risks apply, such as being within 10 m of a river or loch or 50 m of a spring or borehole.
- If the boiler locks out, press reset once. If it locks out again, call an engineer.
- Our domestic oil boiler service is [Between £89-£199. Contact us to arrange a visit.
Why oil boilers need servicing every year
Over a heating season, four things happen:
- The nozzle wears. It turns pressurised oil into a fine spray. As it wears or partly blocks, the flame gets dirtier. Grant specifies a new nozzle at every annual service.
- Filters clog. Water, sludge and debris from the tank starve the burner.
- Soot builds up. It coats the heat exchanger and baffles, so more heat goes up the flue and more oil goes on your bill. OFTEC warns that soot can make a boiler lock out altogether.
- Settings drift. The air and oil mix can only be set properly with a flue gas analyser. Without readings, nobody knows whether the boiler is burning cleanly or producing carbon monoxide.
Grant makes annual servicing a condition of its guarantee and expects the service history if you claim.
What OFTEC registration means
OFTEC runs the main UK registration scheme for oil heating technicians. A registered technician has passed an approved assessment for the work, renews it periodically, and works for a registered business that is insured and inspected by OFTEC.
In England and Wales, OFTEC is also a competent person scheme for self-certifying building work. Scotland uses building warrants instead, so here registration shows the technician has been assessed and their work is checked.
Unlike gas, no law says an oil technician must be registered, so it pays to check on OFTEC's online search. Gas Safe registration does not cover oil.
What a proper oil boiler service includes
We follow the manufacturer's servicing instructions for each boiler, whether it's a Grant, Worcester Bosch Greenstar Heatslave, Firebird or Warmflow. On a typical pressure-jet boiler, a full service covers:
- Tank and supply. A look at the tank, base and bund, a dip test for water, and a check of the oil line and fire valve.
- Oil filter and hose. Filter element replaced or cleaned; braided oil hoses replaced where specified (Grant says annually unless a long-life hose is fitted).
- Burner. Removed and stripped, with the fan, air intake and burner head cleaned.
- Nozzle. Replaced with the size and spray angle specified for that boiler.
- Ignition and flame detection. Electrodes cleaned and set; photocell cleaned and tested.
- Heat exchanger and baffles. Combustion chamber brushed and vacuumed, baffles removed and cleaned.
- Seals and condensate trap. Door and burner seals checked and replaced if damaged; on condensing models, the trap is cleaned.
- Combustion analysis. Pump pressure checked, smoke test done, flue gas readings taken and set to the manufacturer's figures.
- Flue, controls and safety devices. Flue checked for damage and safe clearances; overheat thermostat and controls tested; system pressure and expansion vessel checked on sealed systems.
- Paperwork. Readings recorded in the boiler's service log and on an OFTEC CD/11 servicing and commissioning report, with any defects explained.
If the burner never came out and no combustion readings were written down, you didn't get a full oil boiler service.
How it compares with a gas boiler service
- Who does it. Oil boiler service: OFTEC registered technician recommended. Gas boiler service: Gas Safe registered engineer, required by law.
- Routine parts. Oil boiler service: Nozzle and oil filter, plus hose where specified. Gas boiler service: Usually none unless worn.
- Paperwork. Oil boiler service: OFTEC CD/11 report and service log. Gas boiler service: Manufacturer's service record.
- Our price. Oil boiler service: Between £89-£199. Gas boiler service: £89, see boiler servicing.
Your oil tank and supply
Many oil boiler faults start at the tank. On each service we look for:
- Damage. Splits, bulges or discolouration on plastic tanks; rust or weeping seams on steel ones.
- Water and sludge. Both settle at the bottom and get drawn into the line when the tank runs low.
- Fire valve. It shuts off the oil if there's a fire at the boiler. Scottish building standards guidance expects one on the fuel feed, fitted to BS 5410 and OFTEC guidance.
- Oil line. Supports, damage and weeping joints.
The Scottish rules on domestic oil tanks
Many guides still quote the Water Environment (Oil Storage) (Scotland) Regulations 2006. Those were revoked in 2018 and replaced by SEPA's General Binding Rules, now under the Environmental Authorisations (Scotland) Regulations. For houses:
- Tank of 2,500 litres or less at a private dwelling, used only for heating or cooking: it must be sound enough that it's unlikely to burst or leak, and any tank installed or altered must meet the building regulations. There is no blanket bund requirement.
- Tank over 2,500 litres: the general rules apply, including secondary containment of at least 110% of capacity.
- Tank also serving a business or farm: check with SEPA, as the domestic rule may not apply.
For smaller tanks, Standard 3.24 of the Scottish domestic technical handbook decides whether a bund is needed. An outdoor tank of up to 2,500 litres should have a catchpit or integral bund holding 110% of its contents where it is within 10 m of a river, loch or coastal water; within 50 m of a borehole or spring; where a spill could reach an open drain, a loose manhole cover or a watercourse; where the vent can't be seen from the fill point; or where there's another site-specific hazard. Indoor tanks always need containment. That catches plenty of rural homes on a private water supply or above a burn.
Standard 3.23 covers fire. The guidance is to site the tank at least 1.8 m from the house and 760 mm from a boundary, or use a fire-resisting barrier, on a non-combustible base such as 100 mm of concrete extending 300 mm beyond the tank. A new tank at a house of up to two storeys doesn't normally need a building warrant, but must still comply.
Signs a tank needs replacing
- Oil staining on the base, supports or ground
- A bund holding water or oil
- Oil levels falling faster than your usage explains
- Age: OFTEC suggests seeking advice once a tank is more than 20 years old
OFTEC says home insurance often excludes cleaning up contaminated ground or water, which can cost over £20,000, and gradual leaks or poor maintenance may not be covered. Check your policy and keep your service records.
If you find a leak: turn off the supply at the tank, keep oil out of drains with sand, earth or cat litter, and call your insurer. Ring the SEPA pollution hotline on 0800 80 70 60 if oil has reached, or could reach, a drain, burn or ditch. Don't hose it away or use detergent.
Common oil boiler faults and the reset button
A lit lockout light means the burner tried to fire, didn't detect a flame, and shut down for safety. Before calling us:
- Check there's oil in the tank by looking in or dipping it, as gauges stick.
- Check the boiler has power, the thermostat is calling for heat and the valve at the tank is open.
- Press reset once, as your manual describes. If it locks out again, call an OFTEC registered engineer.
Each failed start sends unburnt oil through the nozzle. OFTEC advises never resetting more than twice, and Worcester Bosch Greenstar oil boilers stop accepting resets after five attempts.
- Locks out on start-up. Common causes: Low tank, blocked filter, water in the oil, worn nozzle, dirty photocell, ignition fault.
- Fires, then cuts out. Common causes: Photocell not seeing the flame, air in the line, part-blocked filter.
- Won't run after the tank ran dry. Common causes: Air or sludge in the line; needs bleeding by an engineer.
- Locks out after a delivery. Common causes: Sludge or water stirred up; Grant advises switching off during delivery and letting the oil settle for about an hour.
- Stops in a hard frost (condensing models). Common causes: Frozen condensate pipe; pour warm, not boiling, water over the outside section.
Oil boilers produce carbon monoxide too. Watch for soot, staining or a smell of fumes at the boiler. CO symptoms include headaches, dizziness, nausea, tiredness and breathlessness. If you suspect CO, switch the boiler off, get into fresh air and call NHS 111, or 999 if someone is seriously unwell. Every Scottish home with a boiler must have a carbon monoxide alarm. If you also have mains gas and smell gas, call 0800 111 999.
Oil heating and Scottish heat policy
Since 1 April 2024, Scotland's New Build Heat Standard has restricted oil and gas boilers in new buildings. It doesn't apply to alterations to existing homes and doesn't stop you servicing or repairing the boiler you have.
If you're considering a switch, Home Energy Scotland offers up to £7,500 in grant towards a heat pump, an optional interest-free loan of up to £7,500, and an extra £1,500 for rural homes, subject to its criteria. Our heating grants guide has the details. Titan Heat doesn't install heat pumps, but we'll keep your oil boiler safe and efficient while you decide.
Oil boiler service cost
Our domestic oil boiler service depends on the level of service required, standard or full strip down. Any extra parts, such as a hose, seals or a photocell, are priced and agreed with you before we fit them.
An oil service takes longer than our £89 gas boiler service because the burner is stripped and parts are replaced as routine, but you can book the standard £89 service and we'll confirm on site if any additional works are required prior to commencing.
How Titan Heat can help
Titan Heat is OFTEC registered for domestic and commercial oil work, and Gas Safe registered (982732) for gas. From our base in Blantyre we service oil boilers across Glasgow, Lanarkshire, Renfrewshire, East Renfrewshire and East and West Dunbartonshire.
- Full annual service to the manufacturer's instructions, with an OFTEC CD/11 report
- Tank, bund, fire valve and oil line checks at the same visit
- Oil boiler fault-finding £85 for domestic premises
- A 1-year parts and labour guarantee on our work
Domestic bookable online For commercial, contact us with your boiler make and model and when it was last serviced. The office is open 8am to 5pm. Running oil-fired plant at business premises? See our guide to commercial oil boiler servicing.
Frequently asked questions
How often should an oil boiler be serviced?
At least once a year. OFTEC recommends annual servicing by a registered technician, and Grant and Worcester Bosch both ask for a service every 12 months, usually as a condition of the guarantee.
How much does an oil boiler service cost?
Our domestic oil boiler service is [CONFIRM: domestic oil boiler service price]. Any extra parts are priced before we fit them.
Do I need an OFTEC registered engineer to service my oil boiler?
It isn't a legal requirement as Gas Safe is for gas, but OFTEC and the manufacturers recommend it. Registered technicians have passed an oil assessment and are inspected.
Does my oil tank need a bund in Scotland?
For a house tank of 2,500 litres or less, only where site risks apply, such as being within 10 m of a river or loch, within 50 m of a spring or borehole, or indoors. Larger tanks need at least 110% containment.
Why does my oil boiler keep locking out?
Usually a low tank, blocked filter, water or sludge in the oil, a worn nozzle or a dirty photocell. Press reset once; if it locks out again, call an engineer.
Can oil boilers leak carbon monoxide?
Yes, if combustion or the flue isn't right, which is why the service includes flue gas analysis. Scottish homes with a boiler must have a CO alarm.
Is there a grant to replace an oil boiler in Scotland?
Home Energy Scotland funds clean heating such as heat pumps, not a like-for-like oil boiler. See our heating grants guide or call Home Energy Scotland on 0808 808 2282.
