General guidance from BUTCH’S Plumbing & Heating. Your appliance instructions and the findings from an individual assessment take priority.
Repeated pressure loss needs investigating
On a sealed heating system, a low pressure reading can stop the boiler operating. Repeatedly adding water does not identify the underlying cause. Possible explanations include a system leak, discharge through a pressure relief valve or an expansion vessel problem. A pressure reading alone cannot confirm the fault.
Useful information to collect
Without removing the boiler casing, note the displayed pressure when the system is cool and again when it is hot. Record any error code and how often pressure drops. Look for visible damp patches around accessible radiator valves and pipework, and tell the engineer if an outside discharge pipe appears to drip. These observations help diagnosis; they are not a reason to adjust safety components.
Follow your own boiler’s instructions
Use the manufacturer’s user guide for the correct operating pressure and any permitted user checks. Boiler models and filling arrangements differ. If you are unsure, ask an engineer. Do not remove the casing, work on gas components or keep topping up a system that is repeatedly losing pressure.
What happens at the appointment?
Tell us how long the problem has been happening, whether pressure rises sharply when the heating is on, and about any recent radiator or heating work. We investigate the symptoms and explain the confirmed findings before quoting additional parts or labour.
Does this mean a new boiler?
Not necessarily. Pressure loss can originate elsewhere in the heating system, and some faults can be repaired. Diagnose the cause before deciding whether replacement makes sense.
Further reading: Worcester Bosch guidance on repeated pressure loss. Check the instructions for your own boiler model.