Display shows water pressure / low pressure error, heater will not fire

Safety first: Allow the system to cool before adding water. Overfilling can cause relief valve discharge.

Step-by-step checks:

• Read the pressure gauge: On combination water heater/boiler models, check the pressure gauge on the front panel. If below 1 bar (cold), the system likely needs topping up.
• Top up via filling loop: Locate the filling loop (flexible hose with two valves) under or near the unit. Open both valves slowly until the gauge reaches 1–1.5 bar, then close both valves tightly. Reset the error on the control panel.
• Check for leaks: Inspect visible pipework, radiators, and the underside of the De Dietrich unit for signs of water leakage. Repair any leaks before repeatedly topping up.
• Bleed air from radiators (if connected): Use a radiator key to bleed trapped air, starting from the highest radiators. Recheck and adjust system pressure afterward.

When to call a professional: If pressure drops repeatedly, or if the pressure sensor or expansion vessel is suspected faulty, contact a qualified technician.