The Jepp Valve is a dedicated solution for filling and repressurising a sealed heating system, such as a combi gas boiler.

Rather than relying on a conventional filling loop, the Jepp Valve provides a compact, purpose-designed solution that simplifies the filling process and creates a cleaner finished installation. The Jepp Valve is designed with a double-check valve that prevents system water, which may contain inhibitor chemicals, from flowing back into the mains drinking-water supply.

There are three types of filling loop commonly found in UK homes:

• External filling loop: a flexible braided hose with one or more isolation valves, connecting the mains water supply to the boiler and heating circuit.
• Built-in filling loop: hidden under or integrated inside the boiler, typically supplied with two taps.
• Filling-key loop: a plastic key inserted into a dedicated slot valve.

To increase system pressure, the user manually opens the valves or taps and watches the boiler pressure gauge until the correct pressure is reached. The valves or taps must then be fully closed.

While filling loops are widely used and familiar to installers, they rely on correct manual operation. Any user error, such as failing to close the filling-loop valves or taps, may result in water loss and over-pressurisation of the boiler.

It is illegal to leave an external filling loop permanently connected. The Water Supply (Water Fittings) Regulations 1999 require a double-check valve and disconnection of the temporary hose after use. The regulation exists to prevent backflow, where heated system water, which may contain inhibitor chemicals, could flow back into the mains drinking-water supply.

Sealed heating systems can gradually lose pressure due to maintenance, bleeding radiators or small losses of water from the system. When pressure falls below 1 bar, your boiler will stop working and you will no longer have hot water or central heating. Water needs to be added to restore the recommended operating pressure. The Jepp Valve is designed to simplify the task of adding water to the boiler without the need to call an engineer or plumber.

When boiler pressure falls below 1 bar, the boiler will stop working, with the consequent loss of hot water and central heating. The boiler will only resume operation when pressure is restored above 1 bar.

The tenant or householder has two options:

• Use a filling loop.
• Call an engineer or plumber.

In the event that an engineer or plumber is called, published 2026 market data suggest a standard gas engineer or plumber call-out cost of around £80, while emergency attendance can exceed £100.

Avoiding one unnecessary low-pressure engineer or plumber call-out during the lifetime of the installation would exceed the incremental hardware cost of a Jepp Valve at an RRP of £58.98.

Although a Jepp Valve can be installed at any time, the most cost-effective time is:

• When installing or replacing your boiler: typical installed replacement boiler cost is in the range £2,500 to £3,000 (average £2,804), while the cost of an external filling loop is in the range £14 to £30 (average £22). Assuming a Jepp Valve cost at the RRP of £58.98, the incremental cost of a Jepp Valve over a conventional filling loop is only about 1.3% of the overall boiler installation cost.
• During your annual boiler service.
• During regular gas-safety checks on gas appliances and flues provided for tenants by housing associations and local authorities under the Gas Safety (Installation and Use) Regulations 1998.
• Whenever an engineer or plumber attends to the boiler.

The terms are often used for equipment that performs the same basic task: admitting mains water to a sealed heating system. A traditional filling loop usually describes a hose-and-valve assembly, while the Jepp Valve provides the filling function through a permanent push-button valve.

Always follow the boiler manufacturer’s instructions. Many domestic sealed systems operate at approximately 1 to 1.5 bar when cold. The Jepp Valve is preset to a maximum outlet pressure of 1.4 bar.

An occasional top-up may be required after maintenance or bleeding radiators. Repeated pressure loss can indicate a fault and should be investigated by a qualified heating engineer.

The Jepp Valve is designed as a permanent boiler filling loop and removes the need to connect a removable flexible hose for routine system topping up.

1. Check the boiler pressure gauge and the pressure recommended by its manufacturer.
2. Press and hold the Jepp Valve button.
3. Watch the gauge as the system refills.
4. Release the button when the required pressure is reached.
5. Check that the pressure remains stable and that there is no sign of leakage.

If the system needs frequent refilling, arrange an inspection by a qualified heating engineer rather than continuing to top it up.

Yes. The domestic Jepp Valve is WRAS Approved under approval number 251215711. WRAS approval confirms that the product has been assessed against the relevant water-supply requirements for its approved use. The Jepp Valve is also patented under patent number GB2527621.

The Jepp Valve can be used in homes and managed properties where a sealed heating system requires a filling loop. Its straightforward operation is particularly useful for landlords and housing associations because an occupier can be shown how to restore pressure without handling a loose hose or several isolation valves. Installation should be carried out by a suitably qualified plumber or heating engineer in accordance with the product instructions and applicable regulations.