Glow-worm F75: pressure sensor and pump communication fault
F75 is not a pressure reading fault so much as a movement fault: the boiler expected the pressure to twitch when the pump kicked in, and it did not.
Key points on an F75 fault
- Recent draining and refilling is a strong clue towards air
- Silt in the sensor port mimics sensor failure exactly
- Pump head is measured rather than assumed
- Cleaning the sensor port sometimes avoids a part entirely
- A system filter reduces recurrence significantly
The engineering behind an F75 fault
That points to a blocked or silted pressure sensor, a pump that is not developing head, or air sitting where the sensor lives. Systems that have been drained and refilled without proper venting throw F75 for days afterwards. Genuine sensor failure is common enough that the part is a stocked item, but pump output should be verified first.
Scope of work
- Domestic boiler installation
- Boiler servicing
- Boiler maintenance and repair
Where we deal with this
Questions we get asked
- Does F75 always mean a new sensor?
- No. A proportion clear with a sensor port clean and proper venting.
- Is my system dirty?
- If we find silt in the sensor, yes — that is a good moment to discuss a flush and filter.
Get an F75 fault looked at properly
Where this leaves you: Vent, clean, measure, then replace. F75 rewards a methodical engineer and punishes parts-swapping.
Use the enquiry form to describe the appliance, fault code and what changed before the problem started.
Related help pages
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- Photocell diagnosisFirebird photocell fault: why a healthy flame still locks out
- Property typeBasement plant rooms: ventilation and flue reach
- Student let servicingHeating servicing in student houses: heavier use, same rules
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