A fire valve shuts off the oil supply if the temperature near the burner rises, using a purely mechanical sensor with no electrical parts. It only works if the sensor is correctly positioned and the valve body is outside the building – and both are frequently wrong.
What it does
Entirely mechanical. A sensor sits close to the burner. If the temperature at that sensor rises above a set point – meaning there is a fire at the appliance – the valve in the oil line snaps shut and stops fuel feeding it.
No electricity, nothing to fail electronically, no user intervention. It is a genuinely good piece of engineering and it asks nothing of you except that it was installed correctly.
Outside the building, in the oil line, before it enters – so that a fire inside cannot damage the valve before it operates. A fire valve fitted indoors next to the boiler is protecting nothing, and it is one of the most common faults we find on older installations.
Why so many would not work
The valve itself rarely fails. What fails is the sensor position, and it fails for mundane reasons:
- The sensor has dropped out of its clip and is dangling behind the boiler.
- It was unclipped for a service and never put back.
- It has been cable-tied to a convenient pipe two metres from where it should be.
- The capillary tube is kinked, which makes the whole device inoperative.
- It was never correctly sited at installation.
- The valve body is inside the building, so a fire would reach it before it operated.
- The valve has seized from decades of never being operated.
- There is no fire valve at all, which we still find on older installations.
In every one of those cases the installation looks entirely normal and the device is decorative.
When it needs replacing
| Finding | Action |
|---|---|
| No fire valve fitted | Fit one. Not optional on an oil installation |
| Valve body inside the building | Relocate to outside, before the line enters |
| Sensor missing, dangling or wrongly sited | Reposition and secure correctly. Frequently just a clip |
| Capillary kinked or damaged | Replace – a damaged capillary cannot be repaired |
| Valve seized or will not operate on test | Replace |
| Valve has operated and been reset | Investigate why. A valve does not close for no reason |
| Age and condition | They are mechanical devices with a finite life. Replacement as part of an oil line renewal is sensible |
A good proportion of what we find needs repositioning rather than replacing, which is a short and inexpensive visit.
Testing it
You cannot tell by looking, because the fault is almost always the sensor position rather than the valve. What should happen at an annual service:
- The valve body location confirmed as outside the building, in the supply line before it enters.
- The sensor located and confirmed secure, correctly positioned close to the burner as the manufacturer specifies.
- The capillary tube inspected along its length for kinks or damage.
- Valve operation checked where the type allows it.
- The finding recorded, so there is evidence it was actually looked at.
If your oil service record has never mentioned the fire valve, it is worth asking whether it was checked. We check it as standard on every oil service – see oil boiler servicing.
How it fits with the rest of the oil line
The fire valve is one component in a supply line that also needs the right materials, protection where it is buried or passes through structure, isolation at both ends, and filtration. The pillar page covering all of it is oil supply pipework and fire valves.
Two practical points that come up together:
- Replacing a fire valve is a natural moment to renew flexible connections at the burner, which have a finite life and are a common source of oil smells.
- If the oil line is being replaced anyway, the fire valve goes with it – see oil line replacement.
Never had the fire valve checked? It is the kind of thing that is fine until the one day it is not.
Questions we get asked about this
How do I know if my fire valve works?
You cannot tell by looking, because the usual fault is the sensor position rather than the valve. It should be checked as part of every annual oil service, with the finding recorded.
Where should the valve be?
Outside the building, in the supply line before it enters, so that a fire inside cannot damage it before it operates. A valve fitted indoors beside the boiler is a common and serious fault.
My sensor is hanging loose behind the boiler.
Then the valve would not operate in a fire. It is usually a short job to reposition and secure it correctly, and it is worth doing promptly.
Do I legally need one?
A remote-sensing fire valve is required on oil installations by the standards installers work to, and its absence is a finding on any inspection. It is also the kind of thing an insurer would be interested in after a fire.
Can the valve be reset if it has operated?
Some types can. The more important question is why it operated – a valve does not close for no reason, and it needs investigating rather than simply resetting.
Is it expensive?
It is a small component. Where the fault is sensor position, the fix is a clip and a few minutes. Where the valve needs relocating outside, it is a short visit.
What happens when you call
Call and describe it
You speak to an engineer, not a call centre. Most jobs can be narrowed down on the phone.
We look at it properly
A real diagnosis before a price, and a straight answer if it is not worth doing.
A written quote
Itemised, so you can see what you are paying for.
The job, and the paperwork
Certificates where the work needs them, and what will need attention next.
Where we do this work
Across Norwich and the whole of Norfolk. If you are on the edge of the county, call and ask — we will tell you honestly whether we are the right people.
- Norwich
- Wymondham
- Dereham
- Attleborough
- Aylsham
- North Walsham
- Cromer
- Diss
- Loddon
- Long Stratton
- Watton
- King's Lynn
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.