Diagnose Why Your Boiler Keeps Losing Pressure

The pressure gauge keeps creeping back down and you are one cold shower away from panicking and booking an emergency call-out. This ranks the likely causes, tells you the signs that confirm each one, and is honest about what you can safely check yourself versus what needs a Gas Safe engineer.

<context>
Your boiler is {BOILER_MAKE_MODEL} and the pressure keeps dropping every few days, currently sitting at [0.5 bar instead of the usual 1.5]. You want to know if this is a quick DIY fix or a call-out job.
</context>

<task>
**Diagnose the likely cause:**
1. List the common causes of gradual pressure loss, ranked by likelihood
2. For each, explain the tell-tale sign that confirms it (damp patches, kettling noise, visible drips)
3. State which of these are safe to check yourself and which need a Gas Safe engineer
4. Explain how to safely top up pressure in the meantime
</task>

<output_format>
- Ranked list of likely causes with tell-tale signs
- Clear DIY versus call-a-professional split
- Short safe top-up instructions
</output_format>