Oil Boiler Warning Signs: What They Mean and What to Do

Signs that need help straight away

• Your carbon monoxide alarm goes off, or someone in the house has symptoms of carbon monoxide poisoning. Follow the steps in the next section.
• You can smell oil fumes. Worcester Bosch's instructions for its Greenstar Heatslave II oil boiler say to put out any naked flames, switch off the electricity supply to the boiler, turn off its oil supply, open the windows and doors, and have an approved contractor fix the fault.
• Oil is leaking. OFTEC says any escape of fuel needs to be resolved urgently (more on leaks below).
• Water or steam is coming out of the safety valve discharge pipe. Grant's instructions say to switch the boiler off and contact your installer or service engineer immediately.
• The pressure on the boiler gauge keeps rising, especially if you keep having to bleed the radiators. Worcester Bosch says this needs urgent action from a heating engineer, because it can mean there is corrosion inside the heating system.

If your carbon monoxide alarm goes off

Carbon monoxide has no colour or smell, so you can't tell if it is around you. That's why the alarm matters. OFTEC's advice if it sounds, or you suspect carbon monoxide:

• Open doors and windows straight away.
• Switch off all fuel burning appliances.
• Leave the building, and don't go back in until it is safe.
• Don't use the appliance again until a competent technician has checked it and confirmed it is safe.

Getting medical help

The NHS says to call 111 if you think you might have symptoms of carbon monoxide poisoning, such as a headache, dizziness, feeling sick, tiredness and confusion, or shortness of breath.

Call 999 or go to A&E if someone has been exposed and is finding it hard to breathe, has suddenly become confused, has lost consciousness, is feeling weak or has chest or muscle pain. Don't drive yourself to A&E. OFTEC also points out that pets may show symptoms before people do.

A smell of oil or fumes

A smell of oil fumes means something needs fixing. Follow Worcester Bosch's steps above and call an engineer. A strong fuel smell around the tank is also on OFTEC's list of warning signs for oil tanks.

Remember that a smell is not a test for carbon monoxide, which has no smell at all. Your alarm is.

Oil leaks

OFTEC says any escape of fuel needs to be resolved urgently, so call a heating technician to find and fix it. In the meantime, keep the damage to a minimum: catch leaking oil in a bucket if you can, or stop it flowing towards a drain with something absorbent such as sand or soil. Never wash oil down a drain.

You may also need to call the national pollution hotline on 0800 80 70 60 (England, Scotland and Northern Ireland), or 0300 065 3000 in Wales. The Oil Care Campaign has more detailed advice on dealing with spills.

OFTEC also advises keeping an eye on your oil level, because a sudden drop could be a sign of a leak. It is worth checking whether your home insurance covers oil spills and leaks, and on what conditions.

The lockout light is on

When a burner detects a fault, or a suspected fault, it shuts itself down. This is called lockout, and most boilers show it with a light or a symbol on the display. On Grant and Warmflow boilers, for example, the reset button on the burner lights up.

Before you reset it, check there is oil in the tank and, on Grant's advice, that the oil supply valve is open. OFTEC says that if it is safe to do so you can look into the tank through its fill point cap, or dip it with a long pole such as a bamboo cane.

A burner can be reset, but OFTEC's advice is never to try more than twice, for safety reasons. Warmflow's instructions say the same. If it locks out again, call an engineer. Your boiler's instructions show how to reset it.

No heating or hot water

OFTEC suggests these checks before you call anyone. None of them involve tools, working with electricity or working at height, but if you are at all unsure, call an OFTEC registered technician.

• Is there oil in the tank?
• Is there power? Check for a blown fuse or a tripped switch in the fuse box, and that the heating's power switch hasn't been turned off by mistake.
• Is the programmer or timer showing the right time and day? A power cut can reset it.
• Is the room thermostat turned up far enough? Turning it up to maximum for a moment shows whether the heating comes on.
• Has the system lost pressure? See the next section.
• Has the boiler overheated? If the pressure was low or zero, it may have. Your boiler's instructions say whether it has an overheat reset you can use. Warmflow warns not to press it while the boiler is still hot, as that damages the thermostat.
• Has the burner gone to lockout? See above.

In cold weather, check the condensate pipe

Grant says a condensate pipe blocked by debris or ice can make the boiler shut itself down, and that you can usually thaw a frozen one yourself with warm water. If none of these checks sorts the problem, OFTEC's advice is that it's time to get a professional in.

Pressure that keeps dropping, or keeps rising

This applies if your boiler has a pressure gauge, which most sealed heating systems do. OFTEC says a reading below 0.5 bar may mean the system needs more water, and to follow your boiler's user instructions to top it up. Only top up when the system is cold and the boiler is switched off.

The right pressure varies by make. Grant gives 0.5 to 1.0 bar for its Vortex Pro, while Worcester Bosch's instructions for the Greenstar Heatslave II say to fill to between 1 and 1.5 bar. Check your own manual.

Topping up now and then is normal. Worcester Bosch says once or twice a year is usual, and to contact your installer if you have to do it much more often, because every top-up dilutes the inhibitor that protects the system from corrosion. Grant suggests looking around the base of the boiler for signs of a leak, and checking the pressure relief pipe, which runs from the boiler to the outside of the house, for signs of water.

Pressure that keeps rising is more serious. See the first section.

New or unusual noises

Grant says a sudden change in the noises your boiler makes can be a sign of an underlying problem. A common cause is limescale building up on the heat exchanger, which overheats and produces steam and bubbling: a whistling sound known as kettling. Grant's advice is to contact your heating engineer if you notice the change.

Smoke, soot and the flue

A white plume from the flue is normal on a condensing boiler. Grant explains that it is condensation vapour, a result of the boiler's high efficiency, and is most noticeable when it is cold outside.

Black smoke or soot is different. OFTEC explains that excessive smoke and partly burnt fuel can cause soot to form inside the boiler's heat exchanger, and that worn fuel nozzles affect combustion and lower efficiency. We couldn't find manufacturer advice on what a homeowner should do about it, so ours is simple: don't try to fix it yourself, and have an OFTEC registered engineer look at the burner.

Keep the flue terminal clear. Grant's instructions say to make sure an outside terminal isn't damaged or blocked, and to cut back any bushes growing over it.

Using more oil than usual

A sudden rise in how much oil you use is on OFTEC's list of warning signs. It can mean a leak, so look over the tank and pipework. It can also come from a boiler that is no longer burning efficiently. Worn fuel nozzles are one cause, and OFTEC lists them among the reasons regular servicing matters.

Look the tank over too

OFTEC's warning signs for an oil tank:

• Rust.
• Splits or cracks.
• Bulging.
• A gauge that has fallen over or stopped working.
• Subsidence in the base.
• A sudden increase in how much oil you use.
• A tank overgrown with plants.
• A strong smell of fuel.

Order oil before you run out

Grant advises ordering oil before the tank runs out, because sludge in the bottom of the tank can be drawn into the fuel lines. If you can, switch the boiler off when the delivery arrives and give the oil time to settle before restarting it. Grant says an hour.

Many faults start with parts that wear

OFTEC's guide to servicing lists parts that wear over time: fuel nozzles, flame sensors that can glaze over and make the boiler shut down at random, and electrodes that may stop it lighting at all. These are among the reasons it gives for servicing regularly.

Related advice

• Carbon Monoxide Alarms and Oil Boilers: What the Rules Say
• Do I Legally Have to Service My Oil Boiler?
• How to Cut the Cost of Heating Your Home With Oil