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Common Main Boiler Problems and Repairs

No one wants to discover that they’re left with no central heating or access to hot water because their boiler has broken down. If you’ve ever had to deal with a misbehaving boiler, you’ll know that it can make your life miserable and, depending on the issue, cost you an arm and a leg to fix. Even minor boiler problems can quickly turn into serious ones, so it’s worth you knowing which issues are common and how to put them right.  

Below, we look at the most common Main boiler problems and the steps you need to take when they occur. 

1. Loud banging noises

Loud or strange noises coming from your Main boiler are a sign of kettling, which is usually the result of a build-up of limescale or sludge on the heat exchanger. Sludge can restrict the water flow to the heat exchanger, then cause the water to overheat and a noise similar to a boiling kettle. A build-up of sludge can occur in your pipework too. 

What to do next: If your heating system is making loud noises because of a build-up of sludge, you need to call out a Gas Safe registered engineer to perform a power flush, which is a cleansing process that removes any limescale or sludge within your system. 

2. Low boiler pressure

If the pressure gauge on your Main boiler is below 1 bar, the system pressure is too low. The boiler pressure may be too low if you have recently bled your radiators. Another common reason for your boiler pressure being too low is a water leak. 

What to do next: Take a look at your boiler, pipes and radiators to see if you can spot a leak or any damp patches, but do not look inside your boiler. If you have not found any leaks, you might need to contact a Gas Safe registered engineer to look inside the boiler. Before you do this, you can re-pressurise the system by following the instructions in your user manual, as long as you feel comfortable doing so. If the pressure drops again after re-pressurising the system, you need to contact a qualified heating engineer.  

3. A boiler leak

When your Main boiler leaks, it is trying to warn you that there is an issue with something inside the boiler itself. A boiler leak is often the cause of an installation fault or a damaged or broken component, like a pump seal. However, you may have an issue with the pressure valve. 

What to do next: If your Main boiler is leaking, you must switch off your heating and the water supply. Then, check the boiler pressure gauge to see if the pressure is too high and the relief valve is leaking. If the pressure is too high, you need to wait for your system to cool down before bleeding your radiators. Once you’ve bled the radiators, switch the boiler back on. If the boiler leak persists, call out a Gas Safe registered engineer to inspect your boiler. 

4. Boiler not turning on

If your Main boiler refuses to turn on or keeps turning itself off, the issue might be a faulty thermostat, low water pressure or a blockage in your system. That said, it may not be anything at all to do with your boiler. 

What to do next: The first thing you can do is check the fuse box and whether there is a problem with your gas supply by turning on your other gas appliances, like your gas hob or oven. If everything else is working fine and your boiler switches on but keeps turning itself off, check the pressure gauge on your system and re-pressurise your boiler if it shows less than 1 bar. Still can’t find the cause? Then you need to contact a Gas Safe registered engineer.  

5. Cold radiators

If you have cold patches on your radiators or they are not heating up at all, the likely cause is trapped air or a build-up of sludge inside your radiators.   

What to do next: The most common reason for cold or partially cold radiators is trapped air, which you can get rid of by bleeding your radiators. If that doesn’t work, you should check that your radiator valves are open or any radiators with a thermostatic valve are on. Still not heating up? Then it’s time to contact a Gas Safe registered engineer to carry out a power flush.  

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