F1 Boiler Fault Explained

A combi-boiler will show a F1 boiler fault code when it doesn't have enough water pressure. Possible causes of the fault involves leaks in the system in most cases. The boiler needs repressurizing after a repair. This is easy to do without the need for a plumber.

F1 Boiler Fault Code Causes

- Water Leaks from Radiators or Pipes and in some rare circumstances the boiler

- Loss of pressure due to bleeding a radiator

We’ve had problems in the past with the pressure on the boiler dropping and for us, the problem was with a connection to a radiator. The pipes had been knocked by the door hitting the pipe into the radiator.

One quick way to check is to wrap tissues around the pipes coming into each radiator. If it becomes wet after 30 minutes or so you’ve found your problem. We would recommend applying this paste around the seal and tightening the nut. 

Leak Repair Sealer
Repeat the test to see if that has fixed the leak.

If there are no leaks you can try the following steps:

- Turn the boiler off
- Wait for the system to cool down (around 20 - 30 minutes)
- Repressurising the system to 1.0 bar
- Turn the boiler back on and recheck the pressure

How long does it take to repressurise a boiler after a F1 Boiler Fault ?

For a combi-boiler with a built-in filling loop, this should only take 10 seconds. It may take longer if your pressure is really low. Keep an eye on the pressure gauge and stop when you get to the 1.0 bar mark. This is enough water to get your combi boiler back up to pressure again. 

If you don’t have a filling loop built-in you may need to buy an external filling loop like this one. The whole process should only take a couple of minutes. Here is a quick video showing you how to do this on a combi boiler.

Repressurising the Boiler with a filling loop

Find the filling loop, a metal hose that has 2 valves – 1 at each end.

Once located, the filling loop attaches to your system.
Open the valves on the filling loop which will allow water from the mains to travel into the heating system. Listen out for water flowing into the boiler, if you don’t hear anything then something isn’t right.

How to repressurise a boiler without a filling loop

A combi boiler system installed as a pressurised system. But, if you have a different boiler system, including water tank. You should never have to repressurise.

Combi boilers are connected to mains to increase the pressure. If your boiler doesn’t have a built-in filling loop, you should buy an external one.

An older combi boiler might have a filling key rather than a filling loop. The key can be inserted into the keyhole and put into the unlock position. Use a spanner or wrench to turn the valve next to the filling key until you can hear water flowing through it. When the pressure is at 1.5 bar, close the valve with the spanner and remove the key by turning it to the lock position. This prevents the valve from being turned on accidentally.

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