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Boiler problems - when is it time to call the experts?

If your boiler's broken, or it's still working but you suspect that there might be something wrong, then in many cases you’ll need to call someone about boiler repair. However, not all regular or combi boiler problems require an expensive engineer callout. At the same time, many problems aren’t as easy to spot as the heating going out, so how can you tell if your boiler needs some care and attention? Here are our top tips for spotting condensing boiler problems and determining if they can be fixed by yourself, or whether it’s time to call in professional help.
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How to troubleshoot common boiler problems

Before calling out an engineer, check to see if your problem is covered below, and whether it’s something you may be able to fix yourself.

My boiler is leaking

The cause of this can vary. Common reasons include a broken valve or seal, badly installed pipework, a leaking boiler pump or possibly corrosion. It may also indicate high temperatures or water pressure, as the boiler has two valves (pressure relief and temperature pressure relief) designed to pass water as a safety precaution. In all cases, you’ll need to call an engineer to diagnose and fix the problem.

My hot water is working but no heating

If your boiler is working but there’s no heating, then check the following:

  • If you have a combi boiler, check it’s not set to hot water only. This setting is commonly used during the summer months.

  • Check your heating controls to see when your boiler is set to switch on – make sure the clock is correct, and that you’ve set the heating to come on at expected times. 

  • Check to see if there’s hot water in the pipes leading to your radiators – if there is, and the radiator is warm at the bottom, but cold further up, it’s likely they need bleeding to remove any trapped air.

Conversely, if your heating works, but your hot water doesn’t, this may indicate the presence of a faulty diverter valve. When working, the valve closes to divert hot water to taps, showers and other outlets when required, then opens up to resume heating your radiators. You’ll need a Gas Safe-registered engineer to fix this.

I’m getting no hot water or heating

Check the following if your boiler is producing no heating of any kind:

  • Pilot light may be out or faulty

  • Your condensate pipes may have frozen

  • There may be issues with your thermostat (see below)

  • A diverter valve may be faulty (see above)

  • Your boiler’s pressure is too low – try repressurising it (see ‘My boiler keeps switching off’ below) before calling out an engineer

My boiler makes a noise when it’s switched on or off

This may not be a cause for concern. It’s normal for your boiler to make certain noises when it comes on or off – these include the sound of the pilot light igniting and the pump circulating water through the boiler’s heat exchanger, for example. However, if this isn’t the case, there may be reason to worry. Common noises requiring additional attention include:

Whistling sounds and banging noises – the result of ‘boiler kettling’, which means due to the flow of water slowing down, it’s being heated to boiling point rather than the temperature set by your boiler, resulting in steam entering the system. Causes include limescale build-up, a faulty thermostat on the boiler (more common in older boilers) or a damaged pump. In all cases, you’ll need to call out a Gas Safe accredited engineer to diagnose the exact cause and suggest a remedy.

Gurgling noises – caused by air getting trapped in the system and mixing with the water. Check your radiators to see if they need bleeding. If they don’t, and it’s particularly cold outside, check the condensate pipe hasn’t frozen.

Droning noises – does your boiler sound like an aeroplane is taking off? This is usually caused by a faulty pump, which will need replacing by a qualified engineer.

Humming noises can be linked to excessively high water mains pressure, a pump sending hot water through the system too fast, or even by the bearings in the boiler fan. In all cases, a Gas Safe-registered boiler engineer will need to be called out.

Whooshing noises are typically caused by one of two reasons: a blockage in the air intake pipe, or an air filter blockage. Again, this will require an engineer callout to fix.

My boiler doesn’t respond to the thermostat

Start by verifying your thermostat isn’t set too low – nudge it up a couple of degrees above room temperature, which should kickstart it into action. If the thermostat is powered by batteries, check they don’t need replacing; if it’s powered by the mains, verify the clock hasn’t been reset by a recent power outage, which would knock its timings off. Also, check the switches haven’t accidentally been knocked out of position, and see if there’s a reset button or instructions to follow via the thermostat’s manual.

If, after all these checks, the thermostat still isn’t working, it may be faulty.

My boiler keeps switching off

Three major reasons for this include a problem with the thermostat (see above), low water pressure or lack of flow. After checking your thermostat and seeing if the radiators need bleeding, try checking the pressure as reported by your boiler. Follow your manufacturer’s instructions to try and repressurise the system; if this fails, you’ll need to call a Gas Safe registered engineer to fix the problem.

My boiler won’t turn on

If your boiler won’t switch on at all, and you’ve determined the trip switch or fuse isn’t to blame, then the problem is likely to be with the boiler’s PCB board. PCB board problems can also manifest themselves in other ways, such as the interface not lighting up, flashing or displaying a specific error code.

While you may be able to fix some errors – for example, memory faults require you to consult your boiler manual for instructions on how to synchronise the PCB with the boiler – others require you to call out an engineer with Gas Safe accreditation. 

How do you diagnose a boiler problem?

First, examine your boiler’s on-screen display. It may have thrown up an error code – if it has, check your boiler manual for what this code means and the steps required to fix it.

If your boiler has a timer, check it’s correct – it may have been reset after a power cut, meaning you may need to set it up again. 

If there’s no power going to the boiler at all, check the fuses to see if your boiler fuse has tripped. If this issue persists after being fixed, you may need to employ the services of an electrician to investigate further.

If you’re on a Pay As You Go tariff, make sure your prepayment gas meter hasn’t run out of credit.

If there’s no gas supply, or you can smell gas, call the National Gas emergency number on 0800 111 999.

If your boiler is working, but exhibiting signs of pressure problems, check its pressure gauge. If it’s lower than one you may have a problem. Verify there are no leaks in the system, then try repressurising the system as outlined in your boiler manual. 

How to prevent issues before they happen

Prevention is always better than cure, particularly when it comes to your boiler where a little ongoing maintenance can save you a huge amount in boiler repair bills further down the road.

What's more, maintaining a boiler is easy. If you sign up for a boiler cover plan with an annual service check included, you can make sure your boiler is inspected at least once a year by a Gas Safe Registered engineer.

Many boilers can freeze up during prolonged spells of cold weather. One way to resolve this is to leave your boiler on permanently when temperatures dip below zero.

You don’t need to have the heating on full blast, but instead of letting it come on and off as required, you can set your programme to reduce the temperature to a minimal level.

A good timer system will allow you to set up different programme configurations, so you can set this up in advance and only activate it when the mercury drops.

Alternatively, focus your attention on the pipes themselves. Any external pipes, including the condensate pipe on a condensing boiler, can freeze in cold weather.

A short-term fix is to pour hot (but not boiling) water onto the pipe to warm it up and melt any frozen liquid inside. You may have to repeat this several times.

A potentially better solution could be to insulate the pipes or, where possible, move more of the pipe indoors.

What to look for when it comes to heating cover

There are many different levels of boiler cover available, ranging from simple breakdown cover for your boiler to a plan that protects the whole central heating system. You should also check to see how much cover each plan offers, as boiler cover typically limits payouts to a maximum amount that usually range from £1,000 to £1,500.

You can only get boiler cover if you own the home so don't try and take it out if you're renting, although you could ask your landlord to take out cover if there are persistent problems.

You will also have limited options available if you try to get boiler cover on a boiler that's more than 15 years old as some insurers don't cover older models.

Find out how to choose the right boiler insurance here.