Are you wondering how to repressurise your combi boiler? We’re here to guide you through each step of the process to ensure everything goes smoothly.
If your combi boiler has lost pressure, it’s usually easy to get the pressure back in its operating range by repressurising your boiler. The good news is that you can repressurise your boiler yourself without having to contact a Gas Safe registered engineer.
Don’t worry if you’ve never had to repressurise your boiler before. We’ve put together a step-by-step guide on how to repressurise your combi boiler with an external filling loop, a keyless filling loop or an internal filling key.
But before you begin, check that the bleed valves on all of your radiators and towel rails are closed to avoid water leaks and prevent your combi boiler from losing more pressure.
Steps on how to repressurise your combi boiler using an external filling loop
If you have a combi boiler with an external filling loop, you will also have a silver hose that connects to the cold water mains valve and the heating system valve.
Step 1 – Locate the filling loop and valves
You can usually find the filling loop (silver hose) below the boiler casing. When you locate the filling loop, make sure it is attached to the cold water mains valve and the heating system valve.
Step 2 – Open the two valves
Next, you need to open the cold water mains valve and the heating system valve, one after the other. You need to leave the valves open until the boiler reaches the correct pressure level, so be sure to keep an eye on the pressure gauge.
Around 1 to 1.5 bars is the ideal pressure level when your heating is off, but you can find the correct pressure for your boiler by looking in your user manual.
Step 3 – Close the valves
When your combi boiler reaches the desired pressure, you can close both valves.
And that’s how you repressurise your combi boiler with an external filling loop.
- Steps on how to repressurise your combi boiler using a keyless internal filling loop
You should consider yourself lucky if you have a combi boiler with a keyless internal filling loop because it makes repressurising you’re your boiler quick and easy.
Step 1 – Search for a blue lever
The first step is to find a blue lever located at the bottom of your combi boiler. It should be easy to spot but consult your user manual if you struggle to find it.
Step 2 – Pull down the lever
Once you find the blue lever, pull it down until the pressure gauge reaches 1.5 bar or whatever the correct pressure level is for your combi boiler (check your user manual).
Step 3 – Let go of the lever
You have to let go of the blue lever as soon as your boiler’s pressure is at the correct level.
That’s it. You’re done!
Steps on how to repressurise your combi boiler using an internal filling key
If you have an older combi boiler, it might come with a filling key, which you need to use to top up the pressure.
Step 1 – Turn off your combi boiler
First, switch off your boiler and allow it to cool down before attempting to repressurise it.
Step 2 – Locate the filling key
The filling key is usually white and in the flap or tray at the bottom of your combi boiler’s casing. Remove the tray, then remove the key. Alternatively, your engineer may have given you the filling key when installing your combi boiler.
Step 3 – Find the manifold
The manifold, usually made from black plastic, links to your cold mains into the boiler and through to your central heating system. You can find the manifold at the bottom of your combi boiler.
Step 4 – Insert and turn the filling key
The filling key will have two white arrows on the shaft, and the manifold will include an open padlock and a closed padlock symbol.
You need to insert the key into the manifold with one of the arrows in line with the open padlock symbol, then turn the key to the closed padlock position.
Step 5 – Let water into your system
Leaving the filling key in the closed padlock position, you need to turn the white plastic nut next to the manifold anticlockwise until you begin to hear water filling the system. Keep an eye on the pressure gauge whist the water fills your appliance, then tighten the nut as soon as the pressure gauge reads 1.5 bar.
Step 6 – Remove the filling key
Before removing the key, grab a rag or cloth to catch any water that may drip from the manifold. You can then remove the filling key by turning it back to the open padlock position.
Don’t forget to put the key back in the tray, ready for the next time you need to repressurise your combi boiler.
What if you add too much pressure to your combi boiler?
If you accidentally add too much pressure to your combi boiler, you will need to bleed your radiators to reduce it and then top up your system again. But if you have gone as far as the red zone on your boiler’s pressure gauge, you may have to drain your boiler heating system.
How often should a combi boiler need topping up?
You may have to repressurise your combi boiler once or twice a year, but you shouldn’t need to do it frequently. If your combi boiler keeps losing pressure, it could be a sign of a problem, like a leak in the boiler itself or somewhere in your heating system. Leaks can cause damage to the components inside your boiler and lead to expensive repairs.
If you have to top up your combi boiler regularly, you should contact a Gas Safe registered engineer as soon as possible to identify and fix the problem.