What to check, in order
- Read the pressure gauge
Baxi says it should be between 1 and 2 bar. With the boiler cold, the needle should sit in the middle of the green area.
- Top up with the filling loop
Follow your user guide, or Baxi's how-to video. Aim for between 1 and 2 bar.
- Look for leaks
Check pipes, radiators and valves for rust, corrosion or staining.
- Don't overfill it
While the boiler heats, Baxi says the needle rises a little but shouldn't go above about 2.5 bar. If it's too high, bleeding a radiator brings it down.
When to call a Gas Safe engineer
If you keep having to top it up, call a Gas Safe registered engineer. Baxi says the expansion vessel may need recharging or replacing. If the pressure relief valve is dripping and the pressure is low, Baxi says it may have debris inside and an engineer will need to clean it out or replace it.
Good to know
- Baxi says it's normal for air to get into the system over time, and cold spots on radiators are the sign. Its advice for low pressure is to bleed the radiators and top up the pressure.
Parts people end up buying
Only if the checks above point to a part. Match it to your model number first: it's on a label on the data badge, usually under the boiler or behind the front cover.
- Radiator bleed keySearch on Amazon
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Checked against
- Baxi: boiler error codes (list for engineers)
- Baxi: what should my boiler pressure be set at
- Baxi: why is my boiler pressure low
Last reviewed September 2026. Manufacturers update their pages, and your manual is the final word.