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How To Repressurise A Boiler [Without Paying An Engineer or Boiler Expert]

Welcome to our 5-minute guide on how to repressurise a boiler.

It will explain not just how to top up your boiler with pressure, but why you should be highlighting the issue at hand; how your boiler is losing pressure.

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Why You Shouldn’t Repressurise A Boiler

Central Heating System Leaks Cause Low Pressure

If you are constantly having to repressurise your boiler in your home or on your property; you have a leak.

This leak isn’t necessarily in the boiler. It could be in any part of the central heating system. For instance, a radiator with a pinhole in it.

However, if it is in the boiler, there’s a chance the water could leak and cause expensive electrical parts in the system to break, such as the PCB (the boiler’s circuit board).

We’ve created guides relating to boiler’s losing pressure, and boiler leaks, in our boiler fault finding guide.

If you’re still struggling with boiler pressure, get a heating engineer to help fix the problem.

Diluting Heating Inhibitor

Inhibitor is a liquid that protects your heating system.

Over time, the inside of radiators, towel rails, and pipework rust. This breaks off, gets broken down and forms central heating sludge.

This sludge can lodge itself in radiators (causing them not to work), the pump, and even the heat exchanger. Those are all things that are expensive to fix.

And, this liquid is leaving the water heater system every time it leaks.

By constantly topping up a boiler, you’ll be diluting this inhibitor, and leaving your heating exposed.

Fix the leak first, then repressurise your boiler in your home.

Key Steps on How To Repressurise A Boiler

# Step 1 – Close All Vents To Seal In Water Pressure

Before you begin adjusting the boiler pressure, check all bleed valves on radiators and towel rails are fully closed.

If they aren’t closed, they’ll leak water, and pressure into your home.

# Step 2 – Find And Check Your Filling Loop

Most new combi boilers will have an external filling loop that’s used to top up the boiler with water, and increase the pressure.

It’s a braided hose with a small valve on it, that’s usually located below the boiler casing.

# Step 3 – Open The Filling Loop

As you open the filling loop, you’ll see the boiler pressure rise.

Refer to your boiler owner’s manual for the exact pressure your boiler needs. But, most boilers will operate at around 1.5 bar of pressure.

# Step 4 – Close The Filling Loop

Make sure the boiler’s filling loop is completely closed after repressurising. If it’s not, it will slowly leak additional water into the boiler, increase the pressure, and the boiler will lockout.

How To Repressurise A Boiler When There’s No Filling Loop

Some boiler systems will operate with a cylinder, designed as a hot water storage tank.

Although the filling loop shouldn’t be fitted there (it should be in view of the boiler’s pressure gauge), there are instances where they are installed on the cylinder.

As above, you are looking for a braided hose, with a small fill valve on it.

What To Do If You’ve Repressurised Your Boiler Too Much

Ideally, you’ll want to drain the boiler system. But, if the pressure is too high by less than 0.5 bar, you can sometimes rectify the problem by bleeding radiators.

Using the bleed key, a bucket to catch the water and towels to protect carpets in your home, open the bleed valve slowly. This will allow water to escape, and boiler pressure in the system to be released.

What’s Next? Still have questions about boiler pressure?

Get a professional engineer to help with repairs and to figure out why you keep needing to top up your boiler’s pressure.

We’re always happy to offer help and advice on how to repressurise any boiler. If you have a problem you need to fix, refer to our boiler fault finding guide.

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