Glow-worm
Chronic System Pressure Loss
Boiler losing pressure daily, user must keep topping up via filling loop
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Leaking radiator or pipework, Faulty expansion vessel, Pressure relief valve passing, Micro-leaks inside boiler
How to Fix / Troubleshooting
Safety: Do not over-pressurise the system above manufacturer limits. Frequent topping up introduces oxygen and can cause corrosion.
- Visual leak check: Inspect all accessible radiators, valves, and visible pipework for damp patches, green staining, or rust marks.
- Check PRV discharge: Observe the external pressure relief pipe while the boiler is running. Any dripping indicates the PRV is passing.
- Monitor pressure behaviour: Note if pressure rises sharply when heating is on (e.g., from 1.0 to over 3.0 bar). This suggests a failed expansion vessel.
- Engineer tasks:
- Check and recharge or replace the expansion vessel.
- Replace a leaking pressure relief valve.
- Pressure-test the system to locate hidden leaks.
Persistent pressure loss should be investigated; it can lead to boiler damage and inefficiency.
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Repair Difficulty
Medium
3/5
Required Part
Expansion Vessel
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