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A number of central heating problems are relatively simple matters, which can be dealt with by yourself without the need for an engineer’s intervention.

Here we have listed common boiler and radiator faults with simple solutions, which you should try before calling for assistance.

Problem: The top of the radiator is cold and the bottom is hot.

Solution: The radiator needs to be ‘bled’, as air has entered the central heating system and become trapped. The air will rise to the top of the radiator, forming a pocket that will stop the hot water from reaching that part. To effectively bleed the radiator, firstly turn off the heating system, in order that no more air is drawn in. Now, armed with a cloth beneath, use a radiator key (or screwdriver if necessary) to slacken the air bleed valve (located at one end toward the top of the radiator). Turn the bleed key a half turn anti-clockwise, which will release the air (there will be a hissing sound). As soon as water (which can be both hot and dirty, so use the cloth) begins to flow, close the air bleed valve by turning it a half turn clockwise. Do not over tighten the bleed valve.

Note that radiators should not require frequent bleeding. If they do, there is an underlying problem with air entering the system, and this should be attended to by an engineer.

Problem: The top of the radiator is hot and the bottom is cold.

Solution: The most permanent remedy to this problem is a procedure called a ‘power flush’; a cleansing process implemented by a pump, which forcibly cleans the central heating system using water and/or chemicals at high velocity but low pressure. This allows for the removal of black iron oxide sludge and ferrous oxide sediment (magnetite), which build up in the bottom of the radiator, preventing it from properly reaching temperature. Other indications of excessive magnetite are noisy boiler pumps, sticking valves, poor warm-up times, intermittent radiator warm-up and boiler over-heating.

Problem: My radiator is cold, but when I bleed it no water comes out.

Solution: This situation can be caused by an airlock, and will most almost certainly be the case if the pipe leading to the radiator itself is hot. Try turning all the other radiators in the house off using the radiator valves, and then try bleeding the problematic radiator again. Alternatively, the problem may be caused by the internal pin in the TRV (which regulates water flow) having become stuck down in the ‘closed’ position. To bring about a ‘quick-fix’ to this situation, remove the TRV head by unscrewing it, and pull the pin gently upwards with a pair of pliers. Invariably though, this problem will ultimately necessitate the fitting of a new TRV.

Problem: Can radiators be painted, and what impact will this have on their performance?

Solution: It is best to paint radiators in ‘radiator enamel’, which is far less likely to discolour with heat over time. Most new radiators already come with a gloss white finish. Painting will have very little effect on performance, as most heat is actually created by convection rather than radiation

Problem: Certain hot water taps do not work initially.

Solution: This usually happens first thing in the morning, and is caused by an airlock: air bubbles rising from the cylinder trapped at the top outlet. Remove the airlock by opening a bath tap. The system will then work until it has had a dormant time for the air bubbles to achieve another ‘airlock’. The underlying problem could be poor pipe-work layout within the property or the pipe-work not being vented correctly where the hot water outlet comes off the top of the cylinder.

Problem: Can I paint copper pipes?

Solution: Yes, you can. However, bare or new copper should first be lightly abraded with emery cloth or wire wool, and then wiped with white spirit in order to remove any preservative or grease.

Problem: I have creaking and rattling sounds in my wall/floor pipe-work.

Solution: As water gets hotter, pipes expand. As the water cools, the pipes will contract. If the pipes are tightly fitted in the wall or floor, they will start to creak as they expand or contract. The pipes will need to be ‘lagged’ in order to prevent this. It may be that the pipes are sitting so tight there is no room for any movement. If under floor pipes rattle, it may be the case that they have not been ‘clipped’ down properly, and are moving too freely during the expansion/contraction process.

Problem: There’s no heating or hot water.

Solution: These checks may help you fix the problem:

  • Check your power supply is working and a fuse hasn’t blown
  • Check the gas hasn’t been turned off or you have enough oil in your LPG tank
  • Check your thermostats and control switches are turned on
  • Check the pump is running
  • Check the pilot light is lit, your boiler manual will tell you how to relight it

If none of this works, you’ll need to call an engineer.

Problem: My hot water is far too hot.

Solution: With a combination boiler, there is usually a hot water temperature setting. Adjust this as necessary. For normal or ‘conventional’ systems comprising a hot water cylinder, there is normally a ‘cylinder stat’ mounted on the side, which should be preset to 55 – 65 degrees.

Problem: My boiler pilot light has gone out. How do I reignite it?

Solution: On most modern boilers, the pilot light will come on automatically when the boiler detects a ‘call for heat’ from a room thermostat or hot water thermostat. If this does not happen, Gas Safe Registered engineer will need to be contacted. Older types of boilers will have a ‘permanent’ pilot light. This may go out for a number of reasons, such as an interruption in the supply, a draught, or a fault with the boiler itself. Before calling professional help, it is worth attempting to re-light the pilot following the instructions issued with the appliance. If these are unavailable, the manufacturer will have usually printed lighting instructions on the inside of the door.

Problem: There is a constant ‘humming’ sound in my pipe-work.

Solution: A constant humming in the pipes is usually attributable to the boiler pump. Fitting anti-vibration brackets may be necessary to reduce the noise. Also, check that the speed of the pump has not been set too high (this is the job of a Gas Safe Registered engineer). A final possible cause of pipe humming is the volume of water that they carry around the system: your existing pipes may be too small for the amount needed.

Problem: How do I top up a sealed system boiler?

Solution: The boiler pressure should be at 1 to 1.5 bar, which will need topping up manually by the filling loop. This is usually under the boiler and may have one or two taps, both of which need to be open, on it and should be a flexible pipe. Fill to 1 to 1.5 bar, then bleed all the radiators and finally refill to 1 to 1.5 bar. Close all taps.