A cold top and a warm bottom is air. A cold bottom is not, and no amount of bleeding will change it.
If the top of a radiator is cold and the bottom is warm, there is air in it and five minutes with a key will fix it. That is the whole job, and no engineer needs to be involved.
A radiator key, which costs about a dollar from any hardware shop, a cloth and a small container. Nothing else, and no need to turn the water off at the main.
Turn the heating off and let the system cool for an hour. Working with hot water under pressure is how people scald themselves, and cold water tells you more anyway.
Find the valve at the top of one end of the radiator, put the cloth under it and the key on it, and turn a quarter turn anticlockwise. You will hear air. When water arrives instead of air, close it. Do not open it further than a quarter turn: it is not a tap and it does not need to be.
Work through every radiator in the house, starting downstairs and finishing at the one furthest from the boiler. Then check the boiler pressure, because letting air out drops it.
Nine times out of ten a cold room is a valve or a balance problem, not a boiler that needs replacing.
Most combi boilers want between 1 and 1.5 bar cold. There is a filling loop under the boiler, usually a braided silver hose with a tap at each end. Open both slowly, watch the gauge, and close them the moment it reaches 1.2. Leaving the loop open is one of the more common causes of a boiler locking out.
If the bottom of the radiator is cold and the top is warm, that is the opposite problem: sludge has settled and the water is not circulating through the bottom of the panel. Bleeding does nothing for it, and it needs a flush.
If one radiator is cold everywhere while the rest are hot, it is usually a stuck valve. If the ones furthest from the boiler are always cooler, the system has never been balanced. Neither is a failing boiler, and neither is worth being quoted a replacement for.
Any of those is a system problem rather than a radiator problem, and it is worth an hour of someone’s time before it becomes a bigger bill.
In this article
Still cold?
A service is $129 fixed and takes 90 minutes. If it turns out to be a valve, we say so rather than quoting you a boiler.
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