Buderus GB142-24 User Instructions page 22

Operating and error messages
Display
1
Test mode -
-A.
Dot displayed in right-hand
bottom corner
Manual operation
-
-H.
Flashing dot in right-hand
bottom corner
Water pressure too low
H 7 P12
/
Alternating display codes
Table 5 Messages in normal operation mode
1
Push the "Service" button to display this operation message.
2
Is shown automatically, i. e. without you pushing a button.
22
Meaning
Boiler in flue gas test mode (chimney sweep mode)
1
Boiler in manual mode
2
H 7
Water pressure is too low (between 3 and 12 psi). The value marked "P"
indicates the current water pressure in psi. Contact the installer.
http://www.buderus.net