Likely causes
- Filling loop left open or passing water
- Expansion vessel has lost its charge
- Fault inside the boiler letting mains water into the heating circuit
What you can safely check
- Check the filling loop is fully closed (both taps shut) and, if it is a removable type, disconnected
- When the system is cold, bleed a radiator a little to bring the pressure back to between 1 and 1.5 bar
- If the pressure climbs again on its own, call us
What our engineer does
We test the expansion vessel and filling loop and fix whatever is letting the pressure rise, including any fault inside the boiler. Anything involving the gas supply, gas valve, combustion chamber, flue, fan, PCB or heat exchanger must be left to a Gas Safe registered engineer and must not be attempted by the householder.
Models this applies to: Baxi 600, Baxi 800, Baxi Platinum, Baxi EcoBlue, Baxi Duo-tec.
Boiler repairs from £90
Diagnosis and a fixed price before the repair. Most faults fixed on the first visit. Gas Safe 925538.
Other Baxi codes
Guidance only. Fault codes vary by model and firmware; anything involving gas, the flue, the fan, the gas valve, the PCB or the heat exchanger must be done by a Gas Safe registered engineer.
