Vokera water heater shows code 12, no hot water, appliance detects low water pressure or flow in primary circuit

How to Fix / Troubleshooting

Safety first: Allow the system to cool before topping up pressure to avoid scalding from hot water discharge.

User steps:

Check the pressure gauge on the front of the heater. If below about 0.8 bar (cold), the system likely needs topping up.
Use the filling loop (usually a braided hose with two valves) to slowly increase pressure to 1.0–1.5 bar, then close both valves fully.
Bleed radiators (if present) and recheck pressure, topping up again if necessary.
If pressure repeatedly drops, there may be a leak; contact an engineer.

Engineer checks:

Test the water pressure switch or sensor for correct operation and replace if faulty.
Inspect the expansion vessel charge and recharge or replace if the diaphragm has failed.
Check for system leaks at valves, joints, and radiators.

Do not leave the filling loop open permanently; this can damage the system and is unsafe.