When Does A Boiler Need Replacing?

Boilers are stalwart devices that should soldier on for many years of faithful service. But, eventually, boilers do reach the point where continued repairs are unrealistic and replacing them is the best course of action.

Boilers are stalwart devices that should soldier on for many years of faithful service. 

But, eventually, boilers do reach the point where continued repairs are unrealistic and replacing them is the best course of action. Boilers typically last 10 to 15 years at least, but it’s not unheard of for old workhorse boilers to reach the ripe old age of 30 years or so. 

Regular professional servicing will extend the life of a boiler, and as long as they’re working efficiently, there’s little reason to replace them in a hurry. However, that isn’t always the case, and it’s certainly possible for a 10 to the 15-year-old boiler to go downhill quickly. 

A problematic boiler older than around ten years may be worth replacing. It depends on the boiler and the type of fault(s) it’s developed. 

Signs your boiler needs replacing

It’s not always easy to tell when a boiler needs replacing. There are a few telltale signs to watch out for, however. Here are signs your boiler needs replacing: 

Higher bills

Old boilers are almost unequivocally less efficient. An older boiler might be as low as G-rated, or 60% efficiency, which is far from the 90%+ efficiency of modern boilers. New boilers must be 86% efficient for gas and 85% for oil to meet Building Regulations. 

It’s often said that boilers older than 10 to 15 years are generally inefficient and costly to run, but this does vary, so it’s worth asking a heating engineer at your next scheduled service. 

Woman wearing grey cardigan bent over piles of bil
Above: Bills higher than you expect? It could be your boiler 

While it’s tricky to tell if your bills are rising because we’ve come to expect them to rise anyway, do try and compare your bills to see if they’re increasing ahead of energy price rises. 

  • Higher bills may indicate worsening boiler performance. 
  • If your bills climb over winter without a change in your gas tariff, it could be the boiler.
  • New boilers have to be at least 85% efficient, but many are 90%+ efficient. 
  • A new boiler will gradually pay for itself compared to running an old, costly boiler. 

Strange smells from the boiler

Boilers should not produce any smells whatsoever. So, if your boiler starts producing a sulphurous, eggy or otherwise unusual smell, then evacuate the building and call the National Grid Emergency Line at 0800 111 999. 

Other strange smells, whether burning smells, hot smells or something else, should also be checked out immediately. When the smell of gas is accompanied, call the emergency line and evacuate the building. 

This might accompany a change to your boiler’s pilot light. If you notice the pilot light turning orange, check to ensure your carbon monoxide alarms are working properly and call an engineer as soon as possible. 

  • Boilers should be odourless.
  • Most gas smells are an emergency - don’t hesitate to call the emergency gas line if you suspect a leak. 
  • Changes to the pilot light might accompany smells. 
  • Never ignore a smelly boiler!

Changes to the pilot light 

Older boilers have a pilot light which lights the main burner. Newer boilers have electric ignition and no pilot light. 

blue boiler pilot light
Above: Some boilers have a pilot light visible through a front panel 

It’s firstly important to say that if you smell gas, you shouldn’t go near the boiler to check the pilot light. Instead, shut off your gas at the mains supply, evacuate the immediate area and call the gas emergency line. 

Pilot lights should burn wholly blue. If they burn orange or have an orange tinge, then shut off the boiler and call a Gas Safe Engineer.

If this is the case, the boiler might emit dangerous carbon monoxide, so check with a meter and keep away from the boiler until you receive advice. Remember, carbon monoxide is odourless and can be fatal. 

  • Changes to the pilot light are signs of existing or imminent faults. 
  • Not all boilers have pilot lights - some have electric ignition.
  • Never ignore changes to the pilot light. 
  • If a strange smell accompanies a change to the pilot light, evacuate the premises and call the emergency gas line. Luckily, this is rare. 

Frequent issues

If your boiler shuts off randomly, displays frequent error messages, stops working shortly after firing up or heats slowly, then it might be worth replacing. 

Boilers shouldn’t need to be repaired yearly - a regular service should keep them working smoothly. If you find yourself calling out the engineer to fix your boiler regularly, then ask if it’s worth replacing instead. 

  • Frequent boiler issues may indicate poor overall function. 
  • It’s sometimes cheaper to replace the boiler than keep repairing it. 
  • If regular servicing doesn't keep a boiler working smoothly, there might be other issues. 
  • Ask a heating engineer for advice. 

Low performance

We’ve already mentioned how higher bills are a red flag for many boilers, but you can also gauge boiler health by observing how well your radiators heat up. 

Above: Poor boiler performance might indicate issues 

It’s worth mentioning that inefficient heating systems may be caused by many things like bad boilers, sludgy radiators and issues with feeding and water tanks. Ask a heating engineer for advice if you notice a general drop in central heating performance. 

  • Poor overall heating performance might indicate numerous faults. 
  • A replacement could be a good choice if your boiler function declines over winter. 
  • Poor performance, accompanied by other issues such as leaks, warrants immediate evaluation by a heating engineer. 
  • Ask a heating engineer for advice. 

Parts problem 

Older boilers may work well enough to keep them going year after year, but it’s possible for some more leftfield or unusual models to develop parts problems that make them harder to service or repair. 

Like with older cars, spare parts can also become expensive and time-consuming to source. In this situation, you might have no choice but to replace the entire boiler. 

  • Old boilers become expensive to repair or service. 
  • Sometimes, sourcing new parts for a boiler might become impossible. 
  • In this situation, your heating engineer might warn you that you’ll need a new boiler soon
  • Replacing the boiler is a sound economic decision in such cases. 

Noisy system

If you notice new sounds coming from your boiler, whether it be a hiss, banging noise or some other noise, then it’s best to call a heating engineer as soon as possible. 

Above: Very noisy boilers should be assessed as soon as possible 

These sorts of issues are often easy to rectify by cleaning the boiler and/or replacing heavily worn parts but might signify the start of a wider problem that warrants boiler replacement. 

  • Heating systems produce some noise, but some noises shouldn’t be ignored. 
  • New or worsening noises warrant an immediate evaluation by a heating engineer. 
  • If you hear noises accompanied by the smell of gas, then evacuate the premises and call the emergency gas line.
  • Noisy systems may be fault-ridden, or it could be a simple issue. 


You should address a leaking boiler as soon as possible. If left unchecked, a leak might cause a potentially disastrous electrical short. In addition, electrical shorts might require the boiler’s entire electronic system to be replaced, which might warrant a new boiler. 

  • Leaking boilers can cause catastrophic short circuits. 
  • In some cases, this could pose a fire risk. 
  • If you notice any water coming from your boiler unit, call a heating engineer as soon as possible. 
  • Never ignore a boiler leak. 

When does a boiler need replacing? 

Some of these situations are an emergency, such as smelling gas or noticing a pilot light issue. 

If you smell gas coming from near your boiler, don’t hesitate to call the emergency gas line.

In many of these situations, it’s sensible to consider replacing the boiler. New boilers are highly efficient and can save money in the long term. They can pay for themselves over time. 

Get in touch today with one of our heating engineers for advice. They will help you weigh up the long-term benefits of replacing a boiler vs repairing and servicing your existing one

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