BoilerFaultCodesThe 6 most common faults
01
HIGH High DIY-safe
Your boiler has detected that the water pressure in your heating system is too high and has shut itself down to prevent damage.
What to try first
Locate a radiator in your home, preferably one upstairs.Use a radiator bleed key to slowly open the bleed valve over a cloth.Release a small amount of water until the pressure gauge on the front of the boiler drops to between 1.0 and 1.5 bar.Tighten the bleed valve and check the boiler display.
02
Block 60 High Engineer
Your boiler’s internal computer has lost the correct settings for how much power it should use, causing it to stop working to protect itself.
Full guide for Block 6003
Block 80 High Engineer
Your boiler has automatically paused its operation because the exhaust fumes inside the unit have become too hot, and it will try to start again once it has cooled down sufficiently.
Full guide for Block 8004
Block 81 High Engineer
Your boiler has detected that a key safety sensor measuring exhaust gases has become unplugged, so it has safely shut itself down to prevent operation.
Full guide for Block 8105
Block 82 High Engineer
Your boiler has detected a faulty sensor reading in the exhaust system and has safely shut down to prevent incorrect operation.
Full guide for Block 8206
Error 00 High Engineer
Your boiler is failing to light the internal flame needed to produce heat and hot water.
Full guide for Error 00on the Atag Q 25S
Pressure relief valvePressure sensorMain control PCBFlue gas sensorHeat exchangerPCB
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Atag shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue