Bleeding your radiators and heated towel rails is a routine yet simple task which is often overlooked by many homeowners & tenants. As many new homeowners aren’t sure how to bleed a radiator correctly & safely, carrying out DIY like this is often left until a Gas Safe engineer carries out a routine inspection and/or service, which can be a problem if an airlock stops radiators working long before an inspection is due. In addition, an airlock can be interpreted as a serious problem and result in a call-out, when a few minutes of simple maintenance can prevent an expensive (and embarrassing) visit by a plumber. Clearing airlocks also improves the efficiency of your radiator and towel rail system.
- Radiator keys (available cheaply from supermarkets or DIY stores)
- Old hand towel or cloth
Checking for airlocks in radiators and heated towel rails
This is best done at the start of a cold season (generally around September or October in the UK), but checking every few months isn’t a bad idea.
To check for airlocks in radiators, switch the system on, making sure the radiator thermostats are all switched on to allow water to flow through the radiators. Once the system is warmed up, check the temperature of both the top & bottom of each radiator in your house with your hand (be careful). If any radiator is significantly cooler at the top than the bottom, then there’s probably an airlock in that radiator, as any air will float to the top. Remember that bathroom radiators and heated towel rails (which generally don’t have a thermostat) are more likely to contain air, as are any upstairs radiators.
Radiators on vs. radiators off
There’s probably a 50/50 split between those who think you should have the heating system ON and those who think it’s safer to have the heating system OFF.
Although having the system ON will make bleeding the radiators quicker and more effective (the pressure of the water will force the air out quicker), you’ve got the increased risk of scalding due to hot water leaking out of bleed valves.
Bleeding a radiator
The bleed valve will be at the top of the radiator. Most standard radiators will have one, but may have two, much like a heated towel rail (bleed valves on towel rails will be right at the top or the rail, facing upwards). Fit the radiator key into the bleed valve (modern radiator bleed valves are a standard shape & size).
Whilst holding the cloth immediately under the valve to catch any water drops, turn the radiator key anti-clockwise – be careful to avoid fully opening the valve, as you could make it difficult to close it again!
If you hear a hissing, then you’re releasing the airlock. As soon as the airlock is removed, water will begin to drip from the valve. Once water drips out, close the valve by turning it clockwise.
Sludge or residue build-up
Some heating systems, particularly older ones, are prone to a build-up of sludge, dirt or rust in some radiators. This is sometimes due to corrosion on the inside of pipes, or due to the fact that the water in heating systems doesn’t need to be “potable” (ie. “safe for drinking”).
If radiators are significantly cooler at the bottom after prolonged use, then something is displacing the water. Although some modern systems can be drained by the homeowner (commercial cleaning solutions are available), older systems will need the attentions of a qualified engineer, particularly as come cleaning products may cause damage, or could reveal more serious corrosion levels which may indicate serious repairs are required urgently.
If you’re carrying out any boiler maintenance, or are unsure (or lack experience or confidence), First Bathrooms always recommend that you consult a suitably qualified professional.
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