Makes we repair
Why a radiator is cold at the bottom
A radiator cold at the bottom and warm at the top usually has sludge settled along its bottom. The sludge is rust and iron oxide from inside the radiators and pipes, with limescale in a hard water area. It collects where the hot water can't push through. Bleeding won't shift it, because air shows at the top of a radiator, not the bottom.
One radiator cold at the bottom can be that radiator's own sludge. Several cold at the bottom at once point to the whole system. For that, Ideal and Viessmann suggest cleaning the system with a power flush, a job for a professional. Sludge also slows the heating and strains the pump, so it is worth a call sooner rather than later. We'll ask how many radiators are cold when you ring. Power flushing: when it helps.
Sources: Ideal's, Viessmann's and Baxi's advice on cold radiators.
A radiator cold at the top
A radiator cold at the top and warm at the bottom has air trapped in it. Bleeding the radiator lets the air out. You may hear the air too. Trapped air can clank or rumble as the heating warms up, or make the boiler gurgle.
Air that keeps coming back is a sign of something more. Glow-worm and Vaillant say to raise repeated bleeding at the boiler's service, as there may be an underlying problem. Worcester Bosch goes further. Radiators that need bleeding again and again while the pressure keeps rising can mean corrosion inside the system, and need a heating engineer urgently. A gurgling boiler, and what each noise usually means.
Sources: Glow-worm's and Vaillant's bleeding guides, Baxi's advice on cold radiators, and Worcester Bosch's Greenstar 4000 user instructions.
Emergency power flushing
Sludge in your heating? We flush it out.
A power flush drives the sludge out of your radiators, pipes and boiler, and we do emergency power flushes all over Greater London.
- Kamco Clearflow CF90, which reverses the flow in an instant to loosen the sludge
- A Kamco magnetic filter, whose magnet pulls the magnetite out of the flushing water
- Sentinel X800 cleaner, which dissolves magnetite and limescale for the flush to carry away
- Inhibitor included, to slow the corrosion that makes sludge
Radiators not heating up at all
Radiators not heating up at all split two ways. Either one radiator stays cold while the rest heat, or none of them warms. One cold radiator points to that radiator. None warming points to the boiler, its controls or the system around it. Viessmann adds a third pattern. Radiators cold downstairs while those upstairs are hot can mean the system needs balancing, so that each radiator gets its share of the hot water.
Cold at the bottom, warm at the top
What the makers link it to
Sludge settled in the radiator.
The first step
Ring us, as bleeding won't shift it.
Cold at the top, warm at the bottom
What the makers link it to
Air trapped in the radiator.
The first step
Bleed it, then check the boiler's pressure.
One radiator cold all over
What the makers link it to
Air, or its thermostatic valve stuck shut.
The first step
Check the valve, then bleed it.
Every radiator cold
What the makers link it to
The boiler, its controls, the pressure, the pump or a valve.
The first step
Check the boiler and the controls, then ring us.
Cold downstairs, hot upstairs
Sources: Viessmann's and Baxi's advice on cold radiators, Glow-worm's advice on hot water but no heating, and Worcester Bosch's Greenstar 4000 user instructions.
What you can safely check
The boiler makers' own guides give a householder these checks for cold radiators. Never take the cover off the boiler, and never touch anything that carries gas.
1. Are the valves open, and the heating on?
The thermostatic valve on each cold radiator should be turned up. The boiler should be set for heating, with the timer on and the room thermostat above the room's temperature. Glow-worm suggests a flow temperature on the boiler of 60 to 70 degrees, so the water is hot enough to warm the radiators.
2. Bleed the radiators cold at the top
Bleeding lets the trapped air out of a radiator. With the heating off and the radiators cool, open the bleed valve at the top end with a radiator key. Turn the key a quarter to half a turn, and close the valve once water follows the hiss. Every step is in the questions at the foot of this page.
3. Check the pressure, and top up
The boiler's pressure drops as the bleeding lets out air and a little water. Read the gauge before you switch the heating back on. Vaillant and Glow-worm ask for 1 to 1.5 bar with the system cold. If the pressure is low, top it up as your user guide shows. Worcester Bosch says not to let it fall below its usual setting while you bleed. The F22 fault code page, for topping up a Vaillant or Glow-worm. The E119 fault code page, for topping up a Baxi or Potterton.
4. Switch on, and feel again
The heating goes back on once the pressure is right. After about an hour, feel each radiator, and bleed again if a top is still cold. A radiator still cold at the bottom, or cold all over with its valve open, needs more than bleeding.
If the makers' checks don't warm the radiators, stop there and ring us. We'll ask what the system is doing.
Sources: Glow-worm's and Vaillant's bleeding guides, Glow-worm's advice on hot water but no heating, and Worcester Bosch's Greenstar 4000 user instructions.
When it needs an engineer
Cold radiators need an engineer once bleeding and the checks above haven't warmed them. Any of these signs needs one straight away:
- More than one radiator is cold at the bottom, a sign of sludge in the system that needs cleaning.
- Radiators need bleeding again and again, or the pressure keeps rising. Worcester Bosch says this can mean corrosion inside the system, and needs a heating engineer urgently.
- The pressure keeps dropping after you top it up.
- No radiator heats, with the boiler on and the controls calling for heat.
- A thermostatic valve whose pin won't move.
- Water around a radiator valve, a pipe or the boiler.
Ring us and describe what the radiators are doing. Finding why the heat isn't reaching them is our Gas Safe registered engineers' job. If you smell gas at any point, open the gold "Smell gas?" bar on this page for the free emergency number. What a heating repair visit involves. Every boiler problem, and what each usually means.
Worth knowing
Glow-worm suggests bleeding your radiators about once a year, starting downstairs, as air rises.
What changes the price of the fix?
The cost of fixing cold radiators depends on the cause. Bleeding and a top-up may need no part at all. A stuck valve, a pump or a motorised valve is a part to fit, and sludge means cleaning the system. The rate is agreed on the call before anyone comes out, and no work is done until you say yes. How our rates work is set out in full.
Do you cover my part of London?
Yes: we fix cold radiators all over Greater London, day and night, in every borough north and south of the Thames. Pick your side of the river to see the areas.
North of the river
Every borough north of the Thames: Barnet and Enfield at the top, Hillingdon in the west, Havering in the east, and central London in between.
South of the river
Every borough south of the Thames: Richmond and Kingston in the west, Bexley in the east, and down through Croydon to Sutton and Bromley.
Questions about cold radiators
How do I bleed a radiator?
Bleeding a radiator takes a radiator key, a cloth and a bowl, with the heating off. The makers' guides give these steps:
- Turn the heating off and let the radiators cool, about an hour, with the thermostatic valves left fully open.
- Start downstairs, as Vaillant and Glow-worm suggest, since air rises. Baxi and Viessmann start with the radiator nearest the boiler.
- Find the bleed valve, usually at the top of the radiator at one end: a small round hole with a square inside.
- Hold the cloth under it, turn the key anticlockwise a quarter to half a turn, and stop turning once you hear the hiss.
- Close the valve, clockwise and not too tight, once water comes out after the air. Discoloured water is normal, Glow-worm says.
- Check the boiler's pressure, and top it up if it has dropped, before you switch the heating back on.
If you keep needing to bleed, ring us, as Glow-worm and Vaillant say there may be an underlying problem.
Would a power flush fix it?
A power flush fixes radiators cold at the bottom from sludge, especially several at once, Ideal and Viessmann say. A flush won't fix air or a failed part. Power flushing: when it helps.
Why is one radiator cold and the rest hot?
One radiator cold while the rest are hot has air in it or a valve stuck shut, Baxi and Viessmann say. Bleed it first. If it stays cold, see that its thermostatic valve is turned up and the pin under its head moves. If it still won't heat, ring us.
The boiler is noisy too: is that the same fault?
A noisy boiler and cold radiators can share a cause. Air in the system makes the boiler gurgle and leaves the tops of the radiators cold, Vaillant and Glow-worm say. Bleeding fixes both. What each boiler noise usually means.
How much does it cost to fix?
The cost of fixing cold radiators depends on the cause, and on the part it needs, if any. You'll know the rate before an engineer comes, as it is agreed on the call. How our rates work is set out in full.
Don't know what has failed? You don't have to.Ring and say what you can see or hear. Finding the fault is our job.
Calls answered 24 hours a day
A real person answers and gives you the rate on the call. No work starts until you say yes, and repairs are guaranteed for 12 months: parts, labour and any return visit.
