Quick answer
Only repressurise a boiler if its manufacturer instructions describe the process and you can identify the correct filling point. Stop if anything is unclear; never open the boiler casing or work on gas components.
Check whether repressurising is appropriate
A low reading can follow radiator bleeding or indicate a leak or fault. Check the boiler manual for the correct cold pressure and whether the model has a user-accessible filling loop. Do not use a generic pressure figure for every boiler.
If pressure is falling repeatedly, find the cause rather than repeatedly adding water. Check accessible pipework and radiator valves for signs of leakage, without touching hot or electrical parts.
Follow the model-specific instructions
- 1Switch the heating off and allow the system to cool as the manual directs.
- 2Identify the filling device using the manufacturer's diagram. If you cannot positively identify it, stop and contact an engineer.
- 3Follow the manual to add water slowly while watching the gauge or display; stop at the specified level.
- 4Close the controls as directed and check for leaks. Note the reading and monitor it. Do not force a stiff control or leave a filling connection open.
Know when to stop
If the pressure rises too high, falls again, or the boiler shows an error, do not keep adjusting it. A leak, pressure relief issue or internal component fault may need investigation.
Never remove the boiler casing or attempt internal repairs. Any work involving gas must be completed by a Gas Safe registered engineer. TraceFix can help investigate water leaks in Birmingham and London; a boiler fault should go to a qualified heating engineer.
When to call a plumber
- You cannot identify the filling control from the manual.
- Pressure will not rise, rises excessively or quickly falls again.
- There is water leaking from the boiler or nearby pipework.
- The appliance displays a fault or you suspect gas or combustion problems.