Quick answer: The Glow-worm F75 fault points to a pump or water pressure sensor problem — the boiler can’t detect the expected pressure change when the pump starts, usually due to a faulty pressure sensor, a stuck pump, or trapped air. This is largely an engineer’s job, with only basic checks safe to do at home.
F75 is one of the more technical Glow-worm faults, with limited DIY options. Here’s what it means so you know what you’re facing. A quick note first: if your Glow-worm is over about seven years old and developing pump or sensor faults like F75, it may be reaching the point where a new boiler installation in Edinburgh makes more sense than ongoing component repairs.
What Does the Glow-worm F75 Error Code Mean?
F75 means the boiler didn’t detect a pressure change when the pump ran — it can’t confirm water is circulating, usually pointing to the pump or pressure sensor.
When the pump starts, the boiler expects the pressure to move. If it doesn’t, F75 flags that either the pump isn’t moving water or the sensor isn’t reading it.
What Causes a Glow-worm F75 Fault?
The main causes are a faulty pressure sensor, a stuck or failed pump, trapped air, or low system pressure.
- Faulty pressure sensor — the most common cause
- Seized or failing pump — not circulating water
- Trapped air in the pump or system
- Low water pressure — check the gauge first
- Blockages restricting flow
How Do You Fix a Glow-worm F75 Error?
Check the system pressure and reset once — but most F75 causes need an engineer, so keep DIY to the basics.
- Check the pressure gauge reads about 1–1.5 bar; top up if low
- Reset once to see if it clears
- Don’t attempt to free the pump or change the sensor yourself
If F75 persists, book a boiler repair — the pump and sensor are internal parts for a Gas Safe engineer.
Is Glow-worm F75 a Pump or Sensor Fault?
It can be either, which is why it needs proper diagnosis — the same code covers both, and testing tells the engineer which part is at fault.
Because the pump and sensor work together, guessing risks replacing the wrong component. Professional diagnosis genuinely saves money here.
Can Servicing Help Avoid F75 Faults?
Yes — servicing checks the pump, pressure and system for the wear and air issues that lead to F75.
A regular boiler service keeps the pump and pressure system in good shape, and an autumn service in Scotland heads off deep-winter breakdowns.
When Should You Call an Engineer for Glow-worm F75?
Call a Gas Safe engineer for any F75 that doesn’t clear after a pressure check and single reset — the pump and sensor aren’t DIY components.
This is a fault where calling early is the sensible first move, not the last resort.
Local Glow-worm Boiler Repairs Across Edinburgh and Scotland
We’re Edinburgh-based and cover central Scotland, and F75 is exactly the pump-or-sensor fault our engineers diagnose properly rather than by guesswork. If your Glow-worm shows F75, get in touch.
Frequently Asked Questions About the Glow-worm F75 Error
What’s the difference between the Glow-worm F75 and F22 codes?
F75 is a pump or pressure sensor fault, while the Glow-worm F22 error is a straightforward low water pressure warning. F22 is often DIY-fixable; F75 usually needs an engineer.
Should I check pressure before assuming F75 is the pump?
Yes — low pressure can contribute to F75, so confirm the gauge reads around 1–1.5 bar first. If pressure is fine and F75 remains, the pump or sensor is the likely cause.
Is F75 related to the F28 ignition fault?
No — the Glow-worm F28 error is about ignition, while F75 is about circulation. They’re unrelated causes, though a boiler showing both warrants a full check.
Can I fix a Glow-worm F75 fault myself?
Beyond checking pressure and a single reset, no. The pump and sensor are internal components for a Gas Safe engineer, and diagnosing which is at fault takes proper testing.
