Flue blockage faults: nests, debris and why boilers lock out
The flue has to remove combustion products completely. When it cannot, the boiler either locks out on its air pressure switch or, more dangerously, spills products of combustion.
A blocked flue explained in plain terms
Jackdaw and starling nests in open terminals are a genuine seasonal problem across rural Somerset, particularly in spring. Sagging horizontal runs collect condensate and restrict flow. Damaged or partially collapsed liners in older conversions do the same. Any flue investigation includes a visual inspection along the whole accessible length and a flue gas analysis at the appliance.
Published business details
- Based at 24 Bristol Road, Radstock, BA3 3EE
- Telephone enquiries: 07516 118198
- Opening hours: Monday to Friday, 8:30am to 5:00pm
What matters most with a blocked flue
- Spring nesting is a real cause of flue restriction here
- Horizontal flues must fall back towards the appliance
- Terminal guards prevent most bird and debris problems
- Staining or dripping at the terminal is worth reporting
- Combustion analysis reveals restriction the eye cannot see
Questions we get asked
- Can I clear a nest myself?
- No. Working at height plus a live combustion appliance is an engineer job, and nesting birds are legally protected in season.
- Would a blocked flue set off my CO alarm?
- It can. Treat any CO alarm activation as an emergency regardless of the suspected cause.
Related help pages
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- Baxi fault codeBaxi E119: low system pressure on a Baxi combi
- Baxi fault codeBaxi E133: gas supply or ignition failure on a Baxi combi
- Fuel qualitySludge and water in an oil tank: symptoms and remedies
- Oil supply componentsOil supply lines and Tigerloop devices: keeping air out of the fuel line
- New homeowner adviceWhy it is worth servicing a boiler soon after moving house
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Where we deal with this
Need help with a blocked flue?
In practice: Flue faults are safety faults. Inspect, analyse and fit a terminal guard where nesting is likely.
For gas work, use a Gas Safe registered engineer; for oil work, use an OFTEC-registered technician.
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