BoilerTroubleshooting2026-02-26
Boiler Pressure Drops Overnight
Overnight pressure loss almost always means a small leak somewhere in the system.
If pressure is fine in the evening but low by morning, a slow leak is the usual cause.
Common causes
A small system leak, a weeping relief valve, or a waterlogged expansion vessel slowly drop pressure overnight.
What to do
Check for damp patches and relief-valve discharge; a technician can trace a hidden leak and check the vessel.
Key takeaways
- Overnight loss = a slow leak
- Check for damp and PRV discharge
- The expansion vessel may be at fault
- Trace the leak rather than top up
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