In short
Every oil-fired Aga has a small metal box beside the burner, usually behind the lower left door or a side panel, that decides how much oil reaches the flame. Most owners never touch it, which is the right instinct. But when the cooker is sulking, understanding what the control valve does, what its levers mean and what the flame is telling you is the difference between a two minute reset and a wasted morning. This guide covers that, and is honest about where the owner’s job ends and the engineer’s begins.
What the oil control valve does
The valve has three jobs:
- Constant level. Oil from the tank enters a float chamber. The float closes the inlet when the chamber is full, so the burner is always fed from the same shallow depth of oil, whatever the level in the tank. This is why it is sometimes called the constant level valve.
- Metering. A thermostat, connected to a sensing phial in the cooker, opens and closes a metering valve so the burner runs harder when the cooker is cooling and eases off when it is up to heat. On a traditional Aga this is the only “control” the cooker has: it runs all the time and the valve keeps it steady.
- Safety trip. If oil rises in the float chamber above where it should, because the burner has gone out and oil has kept flowing, or because the float has stuck, a trip closes the supply. That is what the reset button re-arms.
Most Agas also have a separate fire valve in the oil line near the cooker, a heat-sensitive valve that shuts the oil off if it senses excessive heat. It has its own reset button, and it is easy to confuse the two.
The manual lever
The lever on the front of the valve has two positions, usually marked automatic and manual, or shown by an arrow.
- Automatic (normally to the right): the thermostat controls the oil flow. This is the running position, every day of the year.
- Manual (the other way): the valve gives a fixed low feed that bypasses the thermostat. It is used when lighting a cold cooker and when an engineer is testing the burner. Some owners leave the lever on manual by mistake after a relight, and then wonder why the ovens never come up to temperature or why they overheat.
If you find the lever away from automatic and the cooker is behaving oddly, move it back. The thermostat will take over and the cooker will settle over the next few hours. Our lighting guide shows where the lever should be at each step of a relight.
The reset button
The reset is a small lever or button on the control valve, and pressing it gently down until it clicks re-arms the oil supply after a trip. There is no need to hold it down.
Two rules keep this safe:
- Find out why it tripped. A trip means oil built up in the float chamber. If the burner simply went out for a known reason (the tank ran dry, there was a power cut) a single reset after the cooker has cooled is fine. If it trips again, or trips with no obvious cause, stop.
- Never reset a valve above a hot or oily burner. Look through the lighting flap first. If there is a pool of oil in the burner, or the cooker went out only minutes ago, leave it to cool completely and let an engineer deal with it. Vaporised oil in a hot pot can ignite with a bang when it meets a flame.
The fire valve
The fire valve sits in the oil pipe close to the cooker, often low down behind it, with a heat sensor on a capillary run into the burner area. It shuts the oil off if the sensor gets too hot, which can happen during a bad relight. It has its own reset button, and a tripped fire valve is one of the most common reasons an oil Aga refuses to relight when everything else looks right. Reset it once, cold. If it keeps tripping, the burner is overheating for a reason that needs an engineer.
What the flame should look like
Thirty minutes after lighting, look through the lighting flap in the inner door:
- Correct: a steady blue flame, with the shells (the perforated rings in the burner) glowing a dull orange. Quiet, no smell in the kitchen.
- Yellow and lazy: too much oil for the air available. A dirty burner, a flooded pot after a relight, or the lever left on manual.
- Smoky, with soot on the inner door: poor combustion. The burner needs cleaning, or the flue is not drawing.
- Pulsing or roaring: the flue. A blocked or cold flue, a downdraught in high wind, or a flue terminal that needs attention.
- Small and struggling: oil starvation. Tank level, airlock, blocked filter, or kerosene thickened by frost.
A flame that stays yellow after an hour is not going to right itself. Switch off and book a service.
Why an oil Aga goes out
In the order we find them on call-outs:
- Out of oil, or an airlock. The most common of all. Check the tank gauge; after a delivery the line may need bleeding before the burner will feed. Fill the tank before it gets below a quarter: sludge from the bottom reaches the filter when it runs low.
- Blocked filter or water in the tank. Condensation collects as water at the bottom of an oil tank, and tanks grow a sludge over the years. Both block the filter and the valve. An annual service includes clearing them.
- Tripped fire valve or control valve. See above. One reset once cold; if it trips again, stop.
- Dirty burner. Carbon builds up in the burner over months of running. The flame turns yellow, then unstable, then it goes out. Cleaning the burner is a service job.
- Freezing weather. Kerosene can thicken in exposed pipes during a hard frost, starving the burner. Insulating the oil line and keeping the tank topped up helps.
- Flue problems. A nest, a cracked liner or a storm downdraught can blow the flame out. If the Aga goes out on windy nights, suspect the flue. Our flue installation team sees this often.
- Power cut. The control box and the valve need electricity. A power cut puts the cooker out, and it will not relight itself when the power returns.
What you can do yourself
- Check the tank and the gauge.
- Move the manual lever back to automatic if it has been knocked.
- Reset the control valve or the fire valve once, with the cooker cold and no oil in the burner.
- Relight the cooker following the full procedure, including the 15 minute wait for oil to reach the burner.
- Watch the flame at 30 minutes.
When to call an engineer
- Two failed relights.
- Any smell of oil in the kitchen, or oil pooling in the burner.
- A flame that stays yellow, smoky or pulsing.
- A valve or fire valve that trips repeatedly.
- Soot or condensation at the base of the flue.
- The cooker has not been serviced in the last twelve months.
Oil burners should be looked after by an OFTEC-registered engineer, and a service every six to twelve months is what keeps the flame blue. We service and repair oil Agas across Yorkshire, Cumbria and the North East.
Thinking of leaving oil behind?
A 2-oven oil Aga burns around 40 litres of kerosene a week, and the valve, the burner, the filter and the flue all need attention to keep it running. An electric conversion removes the lot: no oil tank, no deliveries, no burner to clean, and each oven under its own control. Our guide to converting an oil Aga to electric explains what is involved, and the running costs guide compares the bills.
Frequently asked questions
What does the oil control valve on an Aga do?
It meters the oil to the burner. A float chamber keeps a constant level of oil, a thermostat opens and closes the valve so the burner runs at the rate the cooker needs, and a safety trip cuts the supply if oil builds up where it should not. It is also called the oil control box or constant level valve.
What is the manual lever on an Aga oil control valve for?
In its normal position, to the right or marked automatic, the thermostat is in charge and the cooker looks after itself. The other position gives a fixed low feed that engineers use when lighting and testing the burner. For day to day running it should sit on automatic; if it has been knocked, put it back and the cooker will settle over a few hours.
What does the reset button on an Aga oil control valve do?
It re-arms the safety trip after the valve has cut the oil supply. Press it gently until it clicks. If it trips again straight away, or oil has pooled in the burner, do not keep resetting it: the cause needs finding first, and that is an engineer’s job.
What colour should an Aga oil flame be?
Blue, with the shells in the burner glowing orange, about 30 minutes after lighting. A flame that stays yellow and smoky, pulses, roars or leaves soot on the inner door means the burner is not burning cleanly.
Why does my oil Aga keep going out?
The usual causes, roughly in order: the tank has run low or air has got into the line, the filter or valve is blocked with sludge or water from the tank, the fire valve has tripped, the burner is dirty, the kerosene has thickened in freezing weather, a flue problem is upsetting the flame, or a power cut has switched the control box off. A burner that goes out repeatedly needs a service.
Can I relight an oil Aga myself?
Yes, once it is cold. Never relight a burner that has only just gone out: vaporised oil in a hot burner pot can ignite with a bang. Leave it at least an hour, ideally until the cooker is cold, then follow the lighting procedure step by step.
Need an engineer?
If your oil Aga has gone out and will not stay lit, or the flame has turned yellow, call John Wray Range Cookers on 01748 811030 or request a callback below. We have looked after oil-fired Agas across the North for over 30 years.