Error H07

Safety precautions:

1. If you smell gas or see a significant leak, ventilate the area and call your gas emergency number immediately. Do not attempt repairs.

2. Only work on the filling loop and external plumbing; do not open or dismantle boiler internals. Any work beyond topping up pressure or basic visual checks should be done by a Gas Safe engineer.

3. Turn the boiler to standby or off (follow your boiler manual) while you work with the filling loop to avoid accidental ignition. Allow the boiler to cool if it was recently running.

4. Keep towels or a small bucket ready – some water can drip when using the filling loop or removing hoses.

Initial checks homeowners can do:

1. Read the pressure gauge on the boiler display or manual gauge. Cold system pressure should usually be around 1.0–1.5 bar. If it’s below about 0.8 bar (or the red zone) you will likely need to repressurise.

2. Look for visible leaks around radiators, pipework, valves, the boiler body and the PRV discharge pipework. Check beneath the boiler for puddles.

3. Recall whether you or someone recently bled radiators; bleeding will reduce system pressure and needs topping up afterwards.

4. Note whether the boiler is showing other fault codes or if the pump is noisy. If present, mention these to an engineer.

Specific diagnostic and fix steps (repressurising):

1. Identify the filling loop type on your installation: external flexible hose with two valves, an internal keyed filling loop (key stored under a flap), or a keyless internal loop (usually a blue lever).

2. For an external filling loop: attach the hose if it is removable, open the mains cold water valve first and then the second valve to allow mains water into the heating system. Watch the boiler pressure gauge and stop when the pressure reaches about 1.0–1.5 bar (check your boiler manual for the exact recommended pressure). Close both valves securely and remove the hose if applicable. Expect a small drip when removing the hose—wipe it up.

3. For an internal keyed filling loop: insert the key into the port (often under a flap) and turn as directed (align to the open padlock symbol) while watching the pressure gauge. When the pressure is in the correct range, turn the key back to the closed position and remove it.

4. For a keyless internal loop: pull down the blue lever or operate the built-in valve per the manual until the pressure reaches the correct level, then release it.

5. After repressurising, switch the boiler back on and check the heating system for correct operation. Bleed radiators from top to bottom to remove trapped air (start with the highest radiator) and recheck pressure afterwards — bleeding can lower the pressure and may require a second small top-up.

6. Monitor the pressure over the next 24–48 hours. If it holds steady, the immediate issue is likely resolved.

When to call a professional:

1. If the pressure will not rise when using the filling loop, if the filling loop valves leak, or you cannot identify how to repressurise, stop and call a Gas Safe engineer.

2. If the pressure drops again soon after topping up or you find any visible leak, a leaking component (pipework, radiator, PRV) or an internal fault is likely and must be repaired by a qualified engineer.

3. If you see other fault codes, unusual noises, repeated lockouts, or any sign of water coming from the PRV or boiler casing, do not continue DIY work — contact a Gas Safe registered engineer.

Final notes:

Topping up pressure is a common homeowner task and Worcester Bosch materials show it can be done safely without an engineer. However, persistent pressure loss, leaks, or uncertainty about the filling loop or controls always require a Gas Safe registered heating engineer to inspect and repair. If in doubt, stop and arrange a professional visit.