Oil boiler will not start in cold weather: waxing, water and filters
Oil boilers are dependable, but their fuel supply is exposed to the weather in a way that mains gas simply is not.
An oil boiler that fails in cold weather: the short technical version
Kerosene begins to cloud and wax at low temperatures, particularly where a long external supply line runs at ground level. Condensation inside a part-empty tank drops water to the bottom, which freezes in the filter or de-aerator. Blocked filters and failing tank valves complete the picture. Prevention is straightforward: keep the tank reasonably full through winter, service the filter annually and insulate exposed lines.
What we see week to week with an oil boiler that fails in cold weather
Homes on the higher Mendip villages and along the exposed ridge roads see harder frosts than Bath by several degrees on a clear night. If your oil boiler only misbehaves in January, the fault is usually outside the building rather than inside it.
Things worth knowing about an oil boiler that fails in cold weather
- A fuller tank condenses less and gains thermal inertia
- Water in the bottom of a tank freezes before the oil waxes
- Filters and de-aerators are annual service items
- Insulating exposed supply lines prevents most cold starts
- Sludge from an ageing tank blocks nozzles as well as filters
Where we deal with this
Scope of work
- Domestic boiler installation
- Boiler servicing
- Boiler maintenance and repair
Book a visit for an oil boiler that fails in cold weather
The honest position: Winterise the fuel path, not just the boiler. Tank level, filter and line insulation prevent most cold-morning failures.
Call Jamie Crawford Heating on 07516 118198 during the published weekday opening hours.
Related help pages
- Cold weather faultFrozen condensate pipe: the winter fault that looks like a breakdown
- Efficiency faultBoiler short cycling: firing on and off every few minutes
- Pattern diagnosisVaillant F28: what changes between a first and repeat lockout
- Worcester fault codeWorcester A7: sealed system pressure fault on a Greenstar
- Oil combustion testingThe oil smoke test: what it measures and why it matters
- Property typeTwo bathrooms and poor flow: diagnosing the real bottleneck
Questions we get asked
- Should I top the tank up before winter?
- Yes. A fuller tank reduces condensation and gives you buffer if a delivery is delayed by weather.
- Can I add an additive?
- Some anti-wax additives exist, but correct filtration, insulation and tank condition matter more.
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