Start with what you can see
Check the boiler display or gauge, then look around radiator valves, visible pipework and underneath the boiler for signs of water. Do not remove the boiler casing.
- Look for damp patches, drips or staining
- Check whether the pressure rises sharply when the heating is on
- Note any fault code before resetting the boiler
- Do not keep adding pressure if water is escaping
Why pressure can keep dropping
Common causes include a leak somewhere on the heating system, a passing pressure relief valve or a problem with the expansion vessel. Some faults are visible. Others need the boiler and system testing properly.
If the pressure falls again after you have topped it up using the boiler manufacturer's instructions, book a repair. That gives me a much better starting point than waiting until the boiler locks out completely.
When to turn it off
Turn the boiler off and call for help if water is leaking from the boiler, electrics are getting wet, or you smell gas. If you smell gas, call the National Gas Emergency Service on 0800 111 999 first.