Do you want to drain your combi boiler? In this guide, we'll explain exactly how to do it, in simple steps.
There are a whole host of reasons why you may want to drain a combi boiler.
It could be done to remove sediment and other matter that has accumulated toward the bottom of a hot water tank, in an effort to combat frozen pipes or as part of the process of adding a central heating inhibitor.
Whatever the reason may be, we’ve compiled a useful and concise guide leading you through the process of draining your combi boiler.
Let’s get right to it...
Steps Involved in Draining a Combi Boiler
If undertaking the work DIY, you’ll require a bucket, hose, spanner, and of course, a radiator valve key.
Only perform this work by yourself if you have the right skills and knowledge.
1. Shut Off Your Boiler
Before you can drain a boiler, it’s critical that you turn it off. You’ll need to disconnect your combi boiler from its power supply.
If in doubt, check your manufacturer’s guidebook for how you can perform this first step.
Do not move straight on to the next step, however, as you need to give your boiler time to cool down.
2. Find the Drainage Valve and Connect a Hose
You’ll generally find a drainage valve at the lowest point of a central heating system. Usually, this would be toward the bottom of a radiator on the first level of your home.
However, if you’re not sure whether it is, consult a professional for help. In this case, it would make sense to have said contractor drain your boiler too, of course.
Assuming your drainage valve is located inside, it will be necessary to lead the draining water from the system to the outdoors.
Otherwise, you could flood your home! This can be achieved by hooking up a hose pipe to your drainage valve. You’ll then need to lead the other end of the hose to the outdoors.
Make sure to pick a suitable spot. It’s best to place a bucket under the valve in case any water drips out of it when draining.
3. Opening Up Drainage Valve
Now onto the main part of the job. First, employ a spanner to open the drainage valve.
Once you do this, water will begin to drain and make its way through the hose. It will take several minutes to drain your entire heating system.
While doing so, watch the hose pipe closely to make sure it doesn’t detach from your drainage valve as this would lead to an absolute mess with water spewing everywhere.
4. Turn the Bleed Valves on All Upstairs Radiators
After you’ve drained your combi boiler, find your radiator key valve and open the bleed valve of each upstairs radiator in your home.
Keep turning until you notice a hissing noise so that you know the valve is open properly.
By doing this, you are enabling water to head toward the drainage valve.
Once you’re done working on your upstairs radiators, repeat this process on your downstairs radiators.
This will remove the remaining excess water from your heating system.
If your heating system exists in two sections, you’ll have to drain from each side of your property.
5. Retighten the Valves
As soon as the work is complete and you’re sure you’ve successfully drained all water from your home’s central heating system, you can retighten the drainage valve and all open bleed valves.
With all relevant valves rightened, you are free to turn your boiler back on and reconnect it to its power supply. You’ve successfully drained your combi boiler.
6. Refill the System
Obviously, you have to refill your combi boiler once it’s been drained properly. In order to achieve this, first, find the filling loop.
This hooks up the mains water pipe to your central heating pipe. You will generally find it beneath your combi boiler.
It tends to resemble a flexible silver hose and connects two different pipes. If in doubt, check the manufacturer’s guidebook or hire a professional.
If you’ve definitely identified the filling loop, you’ll notice a valve at both ends. Turn each. This will open these valves and let water enter your heating system.
Keep watching the boiler pressure gauge while the valves are open. Generally, you want to wait till the pressure lands between 1.5 and 2.
However, you should still always check with the manufacturer’s guidance. They may recommend a specific pressure to reach on the pressure gauge.
Once you reach the desired pressure, close both valves together.
Benefits of Combi Boiler Draining
It’s best to have your boiler drained around once every year, if not every six months.
Some boiler manufacturers will have specific recommendations for the frequency of draining.
But what are the key benefits of this work?
The advantages of draining a combi boiler include:
Removes sludge and sediment, clearing up your boiler.
Can improve the efficiency and functionality of your boiler.
Should prolong its lifespan.
Helps prevent other issues from arising.
Could keep you clear of unnecessary and expensive repair bills (or at least prolong the duration before you’d face such repair bills).
What to do About a Leaking Combi Boiler
If you want to drain your boiler because of a leak, this should be dealt with by a professional.
A leak must be addressed directly and regardless of how small the leak is, you should turn off your water and contact a professional as soon as possible.
The cause of a boiler leak can include:
The water pressure is too high.
Corrosion issues.
The pump is not sealed correctly.
Wear and tear.
Improperly installed boiler.
It tends to cost between £150 and £400 to have a professional fix a combi boiler leak. This could range from fixing a minor leak to more repair significant work.
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