Vaillant F75: the fault that follows any drain-down
If F75 appeared within a day or two of radiator changes, a power flush, or any work that involved draining the system, air is the prime suspect long before any component. The boiler has not seen the pressure response it expects when the pump starts.
Things worth knowing about an F75 after system work
- Timing next to recent plumbing work points strongly to trapped air
- Bleed every radiator, not just the ones that feel cool
- Venting the pump head needs the wet side of the boiler opened
- Silt disturbed by the work can settle in the sensor port
- Persisting past a full vent moves the suspicion to the sensor
Relevant registrations
- Gas Safe registered for domestic gas boiler work
- OFTEC registered for oil boiler work
- Worcester Bosch Accredited Installer
Understanding an F75 after system work before you spend money
Trapped air sits in the pump head and prevents the small pressure fluctuation the appliance uses to confirm circulation. A full bleed of every radiator, followed by venting the pump itself, resolves the majority of post-work cases. Where the fault continues after thorough venting, the pressure sensor port is checked for silt before any part is ordered, since debris disturbed during the work can lodge there.
Where we deal with this
Talk to us about an F75 after system work
Our advice: Match the fault to the recent work. Air explains most post-drain-down F75 events, and it costs nothing but time to vent properly.
Published opening hours are Monday to Friday, 8:30am to 5:00pm.
Questions we get asked
- Can I vent the pump myself?
- Radiator bleeding is safe to do yourself; opening the pump head is inside the boiler casing and is engineer work.
- How long after work should the fault clear?
- Usually within a day of proper venting. Longer than that warrants a call.
Related help pages
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- Worcester rangeWorcester Greenstar 4000: the entry combi explained
- Sime rangeSime combi boilers: an Italian brand seen occasionally on UK surveys
Services that cover this
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