F37 displayed; low water pressure warning; intermittent operation.

Safety first: Let the system cool before topping up.

• Step 1 – Top up pressure: Use the filling loop to raise pressure to the recommended level.
• Step 2 – Monitor pressure: Check over several days. If it drops again, locate and repair leaks.
• Step 3 – Expansion vessel check: Have a technician check and recharge or replace the expansion vessel if pressure swings are large.