If your radiators are only lukewarm then your rooms will be cold. This is a problem that is very easy to fix.

Potential Causes of a Lukewarm Radiator

  • Is your water hot enough? The water temperature at the boiler might be turned right down, try turning it up and see if that fixes the problem. If increasing the boiler thermostat temperature does not make the boiler fire up immediately then you need a new thermostat, which might need a contractor to fix it.
  • If your home has been extended and it still has the original boiler it could be that the before worrying about the expense of that
  • It could also be the room thermostat not working or badly placed, which can really mess up the distribution of heat with radiators. Try turning it up and listen for the boiler firing up, Replacing a thermostat is a job many amateur electricians can handle safely
  • Radiators will also have a problem heating up if there is a build-up of air within the system. This is the most common cause of a lukewarm radiator. You need a radiator bleed key to let the air out of the system, so that hot water flows into your radiator again.

Bleeding Your Radiators

Turn your heating and hot water off for an hour before you start bleeding any radiators.

Every radiator has a small valve or two near its top that you can turn to let out trapped air. The bleed valves may be on the ends or on the back of the rad. These valves normally have a square nut that you can only turn with a special key. You can buy the key at any hardware shop for pennies.

You should not use a naked flame or cigarette while doing this because the “air” is actually hydrogen gas, which burns explosively in air.

Start at the highest radiator in the house and have a cloth in your hand to soak up any water that sprays out. Locate the key on the bleed valve nut and turn it anti-clockwise. You should hear a hissing sound as the “air” escapes; wait until water starts to spurt out of the valve, then turn it clockwise to close it again.

Repeat this procedure with every radiator, gradually moving from highest to lowest. Turn your heating back on and your luke warm radiator problem should be solved.

Balancing Your Radiators

A central heating system distributes hot water to radiators all around your house using just one pump. Your radiator outputs need to be balanced to give you the desired temperatures in different rooms. Radiators are rarely balanced in a new property because it takes hours to let the temperatures in the different rooms to settle down.

This is a job that any householder can do with a pair of pliers. Each radiator has two valves, one at each end. The On-Off valve is the one you normally turn to turn off a radiator. At the other end, usually with a small dust-cap cover is the Flow Control valve. This one governs how much hot water enters the radiator. If you need any radiator to give out more heat just turn this valve 200 anti-clockwise. Conversely, to reduce the heat output of a rad where the room is too hot just turn it 200 clockwise to reduce the flow of hot water into the radiator.

Repeat this as often as necessary until all your rooms are as warm or cool as they need to be. You can usually have bedrooms at a slightly lower temperature than living rooms, and bathrooms are usually warmer.

Adjusting Your Pump

Your central heating pump is the last component you can adjust to get more heat out of your system. This normally has a dial with three or four settings on. Use a slotted screwdriver to turn the dial to a faster setting. The higher settings will make the pump noise more noticeable and shorten the life of your pump, but as a last resort and as an alternative to a new boiler it is worth doing.

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If you don’t know how to bleed a radiator, find your heating pump or balance your radiators, just ask a friend or relative. These really are very simple jobs that anyone can do themselves.


Silverline - Radiator Bleed Key 2Pk (2Pk
Amazon Price: $1.87 Buy Now
(price as of May 13, 2015)
Corrosion resistant easy grip brass key for bleeding your radiators