What if My Radiator Won’t Heat Up?

A radiator not working as it should is the most obvious sign of something being wrong with your heating system.

The most common problem is that the radiator is hot at the bottom and cold at the top — a sure sign of air in the system. Bleeding the radiator will remove the air and is a simple task. To begin, locate the bleed valve, which is positioned in one of the top corners of the radiator. You’ll need to switch off the circulation pump, located with the boiler, first to ensure that air isn’t sucked into the system when the bleed valve is opened. You can probably open the valve with a screwdriver; if not, pick up a bleed key from your local DIY shed. Have a container or an old towel to hand, and turn the key anti-clockwise a quarter stop. If there is air in the system, you’ll hear it hissing. Once the hissing stops and water starts escaping, close the valve again.

If this bleeding needs to be done frequently, it’s a sign that air is entering your system. This may be due to leaking unions or the pump sucking in air on the boiler return pipe.

There may be instances where you want to replace a radiator or remove it temporarily to decorate behind it. You don’t necessarily need to drain the whole system to do this (although if a new radiator won’t match up to the old fittings, you will) as you can usually isolate the radiator. Start by closing the valves that join the piping to the radiator. Then, unscrew the cap nut that attaches the valve to the radiator. Be sure to have a container to hand for drainage. Next, unscrew the other cap nut that attaches the valve to the radiator, lift the radiator off the wall brackets, and drain the remaining water. You can then reverse this process in order to fit the radiator back into position.

(MORE: How to Replace a Radiator)

How Do I Maintain My Heating System?

Old heating systems go wrong, but there are ways to ensure that problems are kept to a minimum and that maximum efficiency is maintained. Limescale is a huge problem for heating systems in hard water areas (mainly in the South-East). If it begins to layer around the heat exchanger in the boiler it can produce hot spots, causing the exchanger to fail quickly. Rust, of course, can affect steel radiators and is caused by air being drawn into the system; sludge, which is in fact magnetite, can reduce the effectiveness of the pump and form in the bottom of radiators.

In order to check how healthy your system is, drain about a pint of water from it. (You can drain the system by switching off the boiler, turning off the mains water supply to the system and attaching a garden hose to the draincock, which will be located on at least one downstairs radiator). If the water’s clear, the system is OK; if the water is orange, there is rust; if it’s black, you’ve got sludge — and you should drain the whole system and start again.

Adding corrosion inhibitor is a good way to reduce corrosion of this kind. You’ll need around five litres of inhibitor (it costs around £15-20/litre from DIY stores). Add the inhibitor into the expansion tank in the loft (if you don’t have an expansion tank, you can inject it into the radiator) and restore the water supply, then turn on the boiler pump.

In terms of reducing scale, most DIY stores sell electronic inhibitors (they usually cost £30-50). Installation varies by product but it’s generally a straightforward DIY job.

Don’t forget the importance of servicing your boiler. Work on gas or oil-fired boilers has to be carried out by an approved plumber — check the Gas Safe register at gassaferegister.co.uk or the OFTEC list in the case of oil boilers at oftec.org. An annual service should cost around £100 and is required for warranties.

What Do All the Tanks Do?

So you’ve taken on an old house, and – they never mention these on the fixtures and fittings list – a collection of tanks. What on earth do they do and why do you need them?

Traditional (‘gravity-fed’) systems in the UK would have two storage devices. One, a cold water storage tank, would be situated in the loft alongside an expansion tank and would feed cold water into a copper cylindrical vessel where it mixes with boiler-fed water for heating. This copper tank is usually situated in the airing cupboard upstairs. It’s the difference in height between the position of the cold water storage tank and the hot water cylinder that creates enough flow for it to be used in showers, etc. (hence ‘gravity fed’).

You might just have a cylinder in the airing cupboard, in which case this will be a pressurised, ‘unvented’ cylinder (e.g. Megaflo). It has its own heat exchanger and receives cold water directly from the mains (at mains pressure), meaning it doesn’t have to rely on the water from the boiler to heat up incoming cold water.

No tank? That means you have a combination (combi) boiler, which combines production of instant hot water and water for supplying radiators, etc.

(MORE: Boilers Guide)


  • Get your boiler serviced regularly.
  • Identifying problems before they become too serious.
  • Treat the water in your radiators. Try a liquid additive – such as Fernox’s Central Heating Energy Saver F6 – to your system. The additive circulates within the water in the system, helping to improve heat transfer efficiency by allowing radiators to reach the desired temperature more quickly, therefore lowering energy usage without compromising heat output. It’s easy to use for the keen DIYer and costs about £20.

Since 2005, all new boilers – replacement or new installations – have to be condensing. This brings with it added efficiency, but also specific requirements in terms of location that might impact on your heating design (and in some instances whether you can indeed install one). Bear in mind that condensing boilers require a connection to an external flue as well as a drain for the condensate, which means in practical terms that if you are replacing a boiler on an internal wall it will be best relocated to an external wall.

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