How to drain a combi boiler

Combi boilers are among the most common types of household boilers out there. It could need to be drained for a number of reasons. For instance, to avoid frozen pipes during periods of disuse. This can also be necessary when making repairs or alterations to heating systems, boiler parts, radiators, and pipework. 

In this blog, you’ll find a clear step-by-step guide to draining a combi boiler. 

What do you need to drain a boiler? 

Before you start the process of draining the boiler, it’s important to gather some equipment. These tools are designed to allow for drainage without causing water spills or damage to the property’s heating supply system. They include: 

• Bucket 
• Spanner 
• Radiator valve key 
• Hose

Process of draining a combi boiler 

Every boiler will have a slightly different sequence when it comes to draining, which can be due to make, age, and any alterations made to the unit. As a result, regardless of your expertise, it’s always best to consult the manual beforehand. The following process is therefore intended to serve as a rough guide that can typically be applied to most combi boilers: 

1.  First, you must turn off the boiler and disconnect it from the mains power supply. After this has been done, wait for any water in the system to cool down. This can take an hour or two at most.
2. Find the boiler drainage valve. This boiler part is usually located at the heating system’s lowest point, so the best course of action is to examine any downstairs radiators. It can sometimes be found outside the property also.
3. Attach a hose to the drainage valve and place a bucket underneath where it is attached. This will catch any leakage that occurs when the system is being drained. Then, lead the hose outside the property to a road gully grate or a sink.
4. Once you are happy all equipment is secure, open the valves. This includes the drainage valve, as well as the bleed valves on all upstairs and downstairs radiators. Bleed valves indicate they’re open by making a hissing noise. You will need a spanner or wrench to open the valves.
5. Check that water is flowing out the end of the hose to see if the combi boiler is draining effectively. After waiting some time, the water should have stopped. This is the sign the system has been drained fully.
6. Finally, tighten the drainage valve and close all open bleed valves. While the system is empty though, it’s the perfect time to make any boiler repairs and replace faulty boiler parts. 

Refilling a boiler is often done with a filling loop and a boiler filling key. For more information on how this can be done for a combi boiler, read our other piece ‘Do all boilers have a filling loop?’. 

Get boiler spares for combi boilers 

Whether you’re looking for specific boiler part for a job, a variety of spares for a certain combi boiler brand, or repair kits, National Boiler Spares has it all. Contact us today to arrange next day delivery.