What you can check safely
- Read the pressure when the system is cold.
- Inspect radiators, valves and visible joints.
- Look for water below the boiler or at the pressure-relief discharge.
- Record how quickly the pressure drops.
- Photograph any fault code on the display.
How the pressure behaves
| Symptom | What the engineer checks |
|---|---|
| Drops over several days | Small leaks and joints |
| Rises sharply when heating | Expansion vessel and valve |
| Water exits through the relief pipe | Pressure, valve and expansion vessel |
| Boiler locks out | Fault code and system operating conditions |
What not to do
Do not keep topping up the system every day without finding the cause. Do not remove the casing, touch gas connections or bypass the safety valve. If you smell gas, leave the property and call the emergency services from a safe distance.
What to send the heating engineer
Provide the boiler make and model, cold and hot pressure readings, how quickly the pressure falls, the fault code and photos of any visible leak. This helps the engineer prepare for the visit.
Frequently asked questions
What pressure should the boiler show?
The correct value depends on the model and installation. Check the manufacturer’s manual and markings on the appliance.
Why does the pressure rise when the heating is on?
Water expands as it warms, but a large change may indicate a fault that needs inspection.
Should I simply top up the water?
A one-off top-up according to the manual may restore operation, but repeated pressure loss means the cause remains.
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