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Radiator cold at the bottom? Here’s (probably) why with costs to fix

In many cases, radiators become cold at the bottom when something is causing a blockage and preventing the flow of hot water through your heating system. 

A blockage could impact a single radiator or several since the hot water is intended to flow through your entire central heating system. 

Why is your radiator cold at the bottom?

Here are the most common reasons for a cold radiator, along with potential solutions to get your radiator back to normal working function quickly: 

Common cold radiator culprit = sludge

Sludge = Cold RadiatorsSludge is a menacing accumulation of pipework sin, hellbent on keeping your radiator cold at the bottom.

The sludge is formed over time, as water begins to stagnate and combines with the natural metallic debris from the radiator itself and the boiler systems pipes.

Inevitably, this causes a blockage at the bottom of your radiator which doesn’t allow hot water to flow as it should. The result – a cold radiator – probably at the bottom.

Radiator hot at top, cold at bottom? 

So, how do you fix a radiator that’s cold at the bottom? Typically, cold spots are caused by a blockage, preventing the flow of warm water, so here's your options and costs:

How to get rid of blockages in radiators: 

#1 - Chemical flush your cold radiators (and system)

Chemical Radiator Flush

What is a chemical flush?

A chemical flush is a magical blend of intense chemicals, applied to a boilers system pipework and radiators amongst hot water. *Also known as a hot flush.

The chemical element breaks down limescale and stagnated water like a pack of hyenas mercilessly taking down a gazelle and creating a clear pathway for the water within your system and most importantly, at the bottom of your radiator.

Having issues with your combi boiler? Read our boiler problems and solutions for quick troubleshooting guidance. 

Learn all about combi boilers in our what is a combi boiler guide. 

How much does a chemical flush of your ice-cold radiators cost?

Cost: £100-£200

Cost with Heatable: £0.00

If you’re investing in a new boiler through Heatable, your chemical flush will cost precisely nothing.

We include a free chemical flush as standard, with every installation. 


#2 - Powerflush your cold radiators (and system)

Powerflush cold radiators

What is a powerflush?

A powerflush isn’t all so different from a chemical flush but is much more robust. 

High powered machinery will push super pressurised water through your entire heating system including the boiler and radiators, tearing apart any and all debris in its path to leave your heating system as good as new.

For properties with older pipework, powerflushing may not be suitable and in some cases actually cause more harm than good – the high pressure can lead to splits in fragile pipework leaving you with a new problem to throw money at.

How much is a powerflush?

Cost: £400 - £600

*Note – for the previously touched upon risks, Heatable do not carry out power flushes. If you require a powerflush, you should look to arrange this privately prior to purchasing your new boiler from Heatable.


#3 - Manually flush the cold-culprit radiator (DIY)

DIY Radiator Flush

For the DIY crazy or criminally insane, it is possible to manually powerflush your own radiator.

At the risk of your neighbours reporting you to Mulder and Scully – you can isolate the water to your radiator, remove it and blast hot water through it yourself, should the mood take you.

Afterwards, relocate your mind, reattach the radiator and move on with your life. At the very least, your radiator should no longer be cold at the bottom now the sludge has got the hell outta' there.

Want to have your boiler moved to a different location? Check out our "cost of moving boiler" guide.

Preventing cold radiators is better than the cure, always.

Boilers don’t have many legs, so don’t wait until yours is on its last.

To prevent your radiators from getting cold, and to keep your heating system running smoothly, what are the options?

Fit a Magnetic Boiler Filter

A magnetic boiler filter is a staple of many high quality boiler installations.

Fernox Boiler FilterBoiler filters are high powered magnets, usually attached to the pipework directly below or above the boiler – they attract dirt and debris and are a must-have for any boiler, new or old.

Don’t have a boiler filter? Prepare for build up and a cold radiator #nofilter

Fortunately, every single boiler new boiler replacement through Heatable receives a free Adey magnetic boiler filter as standard. Get your fixed quote, online.

Cost: £95.00

Cost with Heatable: £0.00

Flush your radiators and heating system

In addition to the boiler filter you should ensure is included in your new boiler installation, a chemical flush should also be on your checklist.

A new boiler installation (before your shiny new one is caressed on to your wall like an oil painting) is the perfect time to have a chemical flush, cleansing your system of decades of debris and sludge before the new boiler gets to work.

Cost: £100-200

Cost with Heatable: £0.00


Add inhibitor (chemicals)

Fernox Radiator Inhibitor

A chemically induced boiler tonic to further ensure the smooth running of a newly installed boiler. 

Consider an inhibitor the spoon full of sugar required to make the water go down within your new boilers system.

Heatable treat your boilers system with Adey inhibitor chemicals that are included – as standard – with every Heatable boiler installation.

Cost with Heatable: £0.00

Cost: £35.00 ish

Note: Thinking about an immersion heater instead? Read our guide to find out how they compare to combi boilers. 

Options if your cold radiator isn’t heating up at all

If you’re in a situation where you can only dream that your radiator was only cold at the bottom and you’re living in a 100% cold radiator hell – then your predicament does differ.

Here’s what to do:

#1 - Check other radiators

If a number or all of your other radiators aren’t heating up, then it’s probably because your boiler is not working – unless of course, you forgot to switch on every radiator? 

Other broken radiators are unlikely to be a coincidence – chances are, they’re an unfortunate sign you need a new boiler – so make sure it’s a good one, with the aforementioned extras included as standard. 

Get an astronomically low price for that new boiler here.

#2 - Consider the age and condition of your radiators 

Some particularly ancient radiators will understandably have sludge and metallic debris blockages that are simply unavoidable due to the weathering over time.

In these instances, you might not need a new boiler but investing money in a chemical or powerflush could be futile and what’s actually required is a whole new radiator.

Do a quick visual inspection of the radiator that's getting cold, if you can see rust/corrosion on the outside, it'll probably need replacing.

Note: If you have an older boiler and are suffering from lockouts and lukewarm water, you may want to consider whether you have a faulty heat exchanger

Radiator cold at the top?

This is much more unlikely however it can happen.

A radiator that’s cold at the top is probably being caused by trapped air and you can solve that through the strangely rewarding process of bleeding your radiators.

Cold radiator at bottom summary and key points:

A radiator that’s cold at the bottom is more commonly a benign problem, with some simple fixes available.

However, in some instances (particularly if opting for a powerflush) a more costly repair or replacement could be required, such as a faulty diverter valve, and if you have a particularly old boiler or system – a new boiler could well be the more economical choice.

When purchasing a new boiler, always ensure you’re receiving the following within your installation cost:

  • A magnetic boiler filter (Fernox or Adey should be your brand considerations)
  • Pre-installation hot chemical flush (and/or powerflush if your system is VERY old)
  • Inhibitor chemical treatment


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Heatable is registered in England and Wales No. 08804726 (VAT No. GB205805920 ). Trading address is 1 Station Road, Great Sankey, Warrington, Cheshire, WA5 1RH. Heatable acts as a credit broker (not as a lender) and offers credit products through a panel of lenders. Heatable is authorised and regulated by the Financial Conduct Authority (reference no. 805259).

[1] Price based on a like for like combi swap in a 2 bed, 1 bathroom terraced home with a standard flue

[*] Installation dates are subject to installer availability

[ยน] only available on combi boiler installations

Financial Support: If you are in receipt of certain benefits, you may be entitled to claim a free boiler grant.