Filling Loop

A Central Heating Filling Loop is the temporary link between the cold mains and a sealed heating system, sold as a double check valve type, a braided flexible loop or a straight loop, and it suits plumbers and heating engineers fitting or servicing pressurised systems.

You use it to fill the system or top up the pressure on the gauge, then take the hose off again. The double check valve type is a kit that includes the double check valve for the mains side, for a new or upgraded fill point. The braided flexible loop is easy to route in a tight cupboard or between awkward valves, and the straight loop suits valves that line up.

The rules are the thing to check. A domestic sealed heating system counts as a Fluid Category 3 risk, and the usual protection is an approved double check valve on the mains side of the fill point. Water Regs UK guidance says the hose should be disconnected when it is not in use, and in Scotland the Scottish Water Byelaws set out the same practice. Filling loop makers also say not to leave the loop permanently connected.

Open the mains valve first, ease the system valve open and watch the gauge, then close both at the boiler maker’s cold fill pressure. Remove the hose and cap the ends. Find the Central Heating Filling Loop you need in our filling loops range.

Specification

• Sizes: Double Check Valve Type, Braided Flexible, Straight
• Suitable for: Filling and topping up sealed central heating systems from the cold mains

Common Questions

Can I leave the filling loop connected? No. Water regulations and the loop makers say to disconnect the hose after use, so mains water cannot be contaminated by the heating system.

What pressure should I fill to? Follow the boiler maker’s cold fill figure, which is often between 1 and 1.5 bar. Check the manual for your boiler.

Which filling loop do I need? The double check valve type for a new or upgraded fill point, the braided flexible for awkward valve positions, and the straight one where the valves line up.

Why has my boiler pressure dropped? Usually after bleeding radiators, or because of a small leak or a fault with the expansion vessel. If you are topping up often, get the system checked.

Call in at 555 South Street, Glasgow G14 0QX, or order online. We’re open Mon-Fri 8am-5pm, Sat-Sun 8am-1pm.