A boiler filling loop is a pipe that provides a temporary connection between your boiler and the mains water supply to repressurise your boiler and tops it up with water after you have drained the heating system or bled out the radiators. This essential component is not complicated to understand, and this helpful article will explore why a filling loop can be useful and what problems it solves.
Components of a boiler filling loop
A filling loop consists of a braided hose pipe and two valves. One is called a stop valve on one side and a double-check valve on the other.
Why is a filling loop a temporary connection?
A filling loop should only be used temporarily to repressurise your boiler, as leaving it connected longer is against water regulations. This is because the backflow of water into the mains is highly prohibited, as the risk of contamination is greater from a central heating system. Over time, limescale and debris can build up, meaning you could drink the water supplied to your radiators, showers, and taps.
That is why you should not use it as a permanent source but only to repressurise your boiler. If you need to repressurise your boiler more often than usual, there may be a fault with your boiler, and you should get it checked by a Gas Safe engineer.
Types of the filling loop
There are two types of filling loops: the more conventional central heating filling loop, or external filling loop, and the internal filling loop, also called a combi boiler filling loop.
Internal filling loop
Internal filling loops (combi boiler filling loops) are built into the boiler. They consist of two valves, one connected to the boiler and the other to the mains. The stop valve controls the water flow, while the double-check valve prevents water from flowing back into the mains.
The internal filling loop is usually located at the bottom of the boiler. In some combi boilers, there is an easy fill link with a single blue or black lever that is pulled to let the water in and released to stop. If you can’t find an internal filling loop valve in the boiler, it might be under the boiler pipes.
External filling loop
On the other hand, external filling loops are an external connection made with the boiler to repressurise it. They also have two valves: one is used to control the flow of water, and the other is used to prevent the water from flowing back into the mains. The main difference is that the external filling loop is attached outside the boiler and is known as a central heating filling loop.
So, why use a filling loop?
Generally, the main reason to use a filling loop is to repressurise your boiler temporarily. This could be due to the boiler losing pressure below 1 bar, bleeding radiators due to a cold radiator or removing an airlock, leakages, or a problem with the boiler itself requiring more frequent repressurising.
Using an Internal Boiler Filling Loop
First and foremost, you must turn off your boiler. Then, open the hatch of your boiler and attach the filling loop key in the relevant slot. Next, turn on the boiler. Control the flow of water using the control valve and the prevention of water flowing back to your mains will be controlled by the double-check valve automatically.
Remove the key and detach the pipe when the pressure reaches the ideal rating according to your manufacturer’s guidance. Remember, when the knob of the filling loop is perpendicular, it is off; if it is straight lined up, it is on.
Using an External Filling Loop
An external filing loop is almost identical, but you must attach it externally. Then, all the steps are the same: turn off your boiler, attach the filling loop, turn it on, control the flow of water using two valves, and as soon as it reaches the ideal pressure rating, close the filling loop keys, and detach it.
How to Remove a Filling Loop
To remove the filling loop, you must unscrew the ends of both hose valves. You will need adjustable water pliers to turn it anticlockwise and unscrew it with your hand. But make sure the valves are closed before unscrewing it, and as a precaution, place a towel as there may be a little bit of water in the filling loop.
Cost of a Boiler Filling Loop
The boiler filling loop costs range from £8 to £20. It is a worthwhile investment to repressurise your boiler if it is getting old. However, if you need to repressurise your boiler more often than usual, you should consider contacting a Gas Safe engineer to inspect the root of the problem.
The boiler filling loop is a cost-effective and temporary solution to repressurise your boiler. It is relatively straightforward to operate, but relying on it for repressurising is not advisable, as you should identify the cause of the pressure loss and address it promptly.
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