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9 June 2021

Five signs you need a new boiler

Boiler faults can be frustrating, costly and dangerous – but they aren't always obvious. Here are the warning signs that your boiler needs replacing
Jade Harding
Lead boiler

The boiler is one of the most intensively used household appliances – but unless the heating suddenly stops working or your water won’t warm up, faults can go unnoticed.

A boiler breakdown can be frustrating and costly, especially in the middle of winter. But certain failures can also be a danger to you and your family if not spotted in time.

Regular maintenance should help keep your boiler running smoothly. But, like most machines, unexpected issues can always crop up.

Read on to find out some of the tell-tale signs that it's time to consider replacing your boiler.

Need a new boiler? Head straight to our best boiler recommendations.

1. Radiators take longer to heat up

Do your radiators stay tepid or take hours to get hot? This could mean that your boiler is on its way out. Most modern boilers can reach their maximum temperature quickly and produce heat almost instantly.

But it could also mean your central heating system is filled with sludge – this causes blockages and cold spots on your radiators. Dirty water circulating in the system could result in long-term problems with your boiler.

No one wants to sit in a lukewarm home while still paying for the boiler to be working full blast. So if your home takes too long to heat up or your water doesn’t come through as hot as it used to, it might be time for a boiler service or a full replacement.

Arrange for a heating engineer to come and fix the problem. If it's a gas boiler, make sure you look for a Gas Safe registered engineer, or an OFTEC qualified engineer if you have an oil boiler.

You can use Which? Trusted Traders to find a local, recommended heating engineer.

2. The boiler is giving off a bad smell

A healthy boiler will never emit any odour. If it does, it needs to be investigated by a professional right away.

Any faint smells could indicate a carbon monoxide leak. Although carbon monoxide itself is odourless, a smell could be created because the leak is causing the boiler to not burn properly.

Other carbon monoxide warning signs that shouldn’t be ignored include:

  • The boiler is burning a yellow flame instead of a crisp blue flame
  • Dark soot staining on and around the appliance
  • Pilot light that frequently blows out
  • Increased condensation inside windows.

Carbon monoxide can be extremely dangerous and potentially fatal to you and your family. Symptoms of carbon monoxide poisoning include headaches, shortness of breath, nausea and unconsciousness.

If you notice any of these warning signs, you should evacuate your home immediately and call the emergency gas line on 0800 111999 to inspect the leak safely. You and anyone else who have been in the property should be checked by a doctor. If you have a pet, take it to the vet, too.

Although there can be signals pointing to a leak, the best way to ensure it is detected as soon as possible is by installing a CO alarm in your home.

A fifth of all the carbon monoxide detectors we tested were so unreliable and dangerous that we labelled them Don’t Buys. Ensure you get a model you can trust by looking at our Best Buy carbon monoxide detectors.

3. Your energy bills are increasing

If your bills are increasing faster than normal, it could be down to an inefficient boiler. As a heating system gets older, it can lose its efficiency and start to cost more to run.

An easy way to check your boiler’s efficiency is to look at the rating on its ErP energy label; these labels have a seven-point colour scale, starting from dark green (A-rated) down to red (G-rated), with the most efficient boilers being green.

An A-rated boiler is the most efficient, at 90%, while a G rating represents less than 70% efficiency. If you replace an old G-rated boiler with a modern A-rated boiler that has a full set of heating controls, the Energy Saving Trust estimates you’ll save around £320 a year on your gas bill.

If you’re trying to pick the most efficient type of boiler, then opt for a modern condensing system – find out more in our guide to condensing boilers.

If you’ve upgraded your boiler and your bills are still rising, you might want to consider switching your energy supplier. Use our independent switching site, Which? Switch, to compare energy prices and find the best energy deal.

4. Your boiler is leaking

If puddles appear around your boiler, you should take immediate action. Internal parts may be faulty or have started to disintegrate.

A leak can lead to further problems, such as rust and corrosion, as well as structural damage to your home. It will also mean that your heating will be inefficient. Think of the wasted water, too.

Avoid paying more for your heating and water, as well as preventing damage to your home, and call your engineer out quick.

Our expert advice will help you to buy the best boiler and find the right model and size for your home.

5. Your boiler is making funny noises

Your boiler will make a noise when firing up, but this should be no more than a low and constant hum that most of us won’t even notice.

But banging, clunking and whirring are the sounds you don’t want to be hearing. These could indicate a number of issues, from a broken valve to heat pump problems. Or, it could just be down to general wear and tear.

Always switch the boiler off first – turning it off could help to stop any further damage – and call out an engineer. The boiler issue could be minor and easily fixed but it’s important to make sure the appliance is safe for use, too.

You can use Which? Trusted Traders to find a local, recommended heating engineer. Or you can use our free Trader search tool below.