Adjust only in increments of 1/8 turn and wait approx. 1 minute after each adjustment
until the value stabilises.
Only for liquid gas:
Adjust only in very small increments (approx. 1/16 turn), and wait approx. 1 minute after
each adjustment until the value stabilises.
10 Troubleshooting
10.1 Logical fault finding procedure
These checks must be carried out before attempting to use the fault finding guide.
1. Carry out electrical safety checks (see section 4 ‘Wiring system’).
2. Check that the external electricity supply to the boiler is on, and a supply of 230 V˜ is
present between boiler terminals ‘L’ and ‘N’.
3. Check that the gas supply to the boiler is on, that it has been correctly purged and that
an inlet pressure of 20 mbar is available at the gas valve. (See section 5 ‘Gas Supply’).
4. Ensure the heating system is full of water and the system design pressure is attained.
(sealed systems only). If not, refill and vent the system. Ensure any flow and return
isolating valves (if fitted) are fully open.
5. Set the central heating temperature to maximum.
6. Set the domestic hot water temperature to maximum (Only if additional Vaillant
accessories are fitted).
7. Check that all external controls are on and calling for heat (if no external controls are
fitted, boiler terminals 3 and 4 must be linked). Check that the boiler anti cycling
economiser is not engaged.
10.1.1 Status codes
The status codes that you can see on the display provides information about the current
operating condition of the appliance.
The display of the status codes can be called as follows:
● Press the “i” key.
The display shows the status code, e.g. S.4 for “Burner mode - Heating”. The display of the
status codes can be cancelled as follows:
● Press the “i” key.
● Do not press any key for approx. 4 minutes.
The current heating flow temperature appears in the display again.
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