James Elston

Published April 9, 2024

Knowing how to check your boiler in between its annual boiler service can save you a lot of money on unexpected costly repairs.

Checking your boiler for any faults or leaks is quite easy once you know how to do it, which is why Eco Happy has crafted this helpful guide.

Read on to discover how to check your boiler, how often to perform checks, and when to call out the professionals.

Understanding Your Boiler

Before you can start checking your boiler, you first need to know what type of boiler you have:

  • Combi boilers: Combination boilers are compact boilers that heat water directly from the mains.
  • System boilers: These boilers heat water from the mains and then store them in a hot water storage tank for use.
  • Regular boilers: Conventional or regular boilers use a cold water tank (in the loft) and a hot water storage tank.

Different boilers also work with different fuel sources to provide hot water for your heating system and taps:

  • Gas boiler: This is the most common type in UK homes and uses natural gas from the main grid for efficient heating.
  • Oil boiler: Commonly found in off-grid areas, it burns oil to generate heat.
  • Electric boiler: It is a clean alternative as there are no exhaust gases, but can be more costly to operate.
  • Biomass boiler: Eco-friendly boilers that use wood pellets or other organic materials to heat the water.

You also need to have a basic understanding of how a boiler works before you can perform any maintenance checks. Although different boilers have different workings based on the type and fuel source, here’s a quick breakdown of how a boiler works:

  1. Water enters the system from the mains (combi and system boiler) or a cold water tank (conventional boiler).
  2. The water is heated using the fuel source (gas, electricity, oil, biomass).
  3. If you have a condensing boiler, exhaust gas is recaptured to heat more water. With non-condensing boilers, these gases are released through a flue.
  4. The hot water is either directly circulated to your radiators and taps (combi boilers) or it is stored in a hot water storage tank for later use (system and conventional boilers).

Of course, the technicalities of boiler functioning go much deeper than that, but for simple at-home boiler knowledge, you only need to know the basics.

Checking Your Boiler

Even though you schedule an annual service each year, you won’t regret checking your boiler regularly. If you spot minor concerns before they become major issues, you can cut down on your boiler service cost or avoid having to call out an emergency heating engineer.

There are two main ways in which you can check your boiler – you can perform visual checks of the different components, and you can check the performance of your boiler.

Visual check

Before you get started, prepare a torch or headlamp as well as a dry cloth if you have to wipe down any wetness.

Also, it is important to never dismantle your boiler yourself. If you spot anything that needs repairing, it is best to contact someone with experience in fixing gas appliances, like Gas Safe engineers.

Here’s a step-by-step guide to visually inspecting your boiler:

  1. External inspection:
    1. Check the boiler casing for any signs of damage, rust or leaking water.
    2. Check if the flue is free of any blockages or debris.
    3. Check that all the connections and pipes going into the boiler is secure.
  2. Internal inspection:
    1. Only perform this check on visually accessible internal components.
    2. Turn off the boiler before you take off the boiler cover.
    3. Find the pressure gauge and note the boiler pressure. It should be between 1 and 2 bars.
    4. Look for signs of wetness or rust that could indicate a water leak.
    5. Inspect the condensate pipe (if you have a condensing boiler) to make sure it is blockage-free.

Don’t attempt to adjust or repair any of the internal components yourself, unless there are clear instructions in the boiler manual on how to do it.

  1. Take notes: As you perform your inspection, it will be helpful to take notes. You can then report your findings at your next boiler servicing (if it is minor) or discuss it with the heating engineer if you have to schedule an emergency one-off boiler service.

Performance check

Never perform any gas or electrical checks yourself. These should be done by a Gas Safe registered engineer who performs your electric or gas boiler service. However, you can check a couple of the components of your boiler to ensure it is still working optimally.

  1. Pressure gauge:
    1. Your pressure gauge will most likely be a circular dial with a needle. Locate it to check the pressure.
    2. When the boiler is off and cooled down, the pressure gauge should be between 1 and 1.5 bar.
    3. If the pressure is below this range, you can repressurise your boiler (the manual should come with instructions or you can read our guide on what to do when your boiler is losing pressure).
  2. Heating system:
    1. When the heating system is running, check that all the radiators are heating up evenly. Feel around the radiator (specifically the top and bottom) to check for cold spots.
    2. If there are cold spots, you have to bleed your radiator as air might be trapped in the system.
    3. If bleeding your radiators doesn’t fix the issue, consider calling in a heating engineer to come balance your radiators.
  3. Thermostat:
    1. This might seem obvious, but start by checking that your thermostat is set to your desired temperature. If your house feels cold, it might just be because the thermostat isn’t set properly.
    2. If you have a modern or smart thermostat, it should be indicated by the lights on the thermostat if the heating system is working correctly. Consult your user manual if you’re unsure.
  4. Hot water:
    1. The simplest way to check whether your boiler is functioning correctly is to turn on a hot water tap and check the temperature.
    2. If the water is not heating up, or there is a long delay before the hot water starts running, there might be a problem with the thermostat or heat exchanger.

Early Warning Signs

Even though it is good to regularly check your boiler, there are some signs that might tell you it is time to call in a profession boiler engineer to get beneath the boiler cover and see what’s happening:

  • The pilot light keeps going out
  • You need to often restart your boiler
  • Your water pressure is dropping
  • The radiators are not heating consistently
  • Hot water temperature fluctuations
  • Boiler noise

When To Call A Gas Safe Registered Engineer

When it’s time to get your boiler serviced, you’re going to have to call in the pros. Boilers usually require an annual service to make sure the boiler is functioning correctly.

But, when should you call an expert to come check your boiler after you’ve performed your checks?

  • Loud noises: Modern boilers tend to run silently, so if your boiler is clanging, banging or gurgling, you need to call out a pro. It could be caused by limescale and debris buildup, a faulty pump, or loose parts.
  • Changes in flame colour: Your boiler’s pilot flame should be blue. If the flame is yellow or orange, you have incomplete combustion, and carbon monoxide might be leaking. Switch off the gas supply, ventilate the room, and contact a Gas Safe Registered engineer.
  • Leaks: Any visible water leaks may need an experienced plumber to fix. Gas leaks are another big concern. If you suspect a gas leak, immediately call in a Gas Safe professional.
  • Performance issues: There are several issues that will require Gas Safe engineers to come take a look at your boiler, including if the pressure is fluctuating, radiators remain cold, or the water remains lukewarm.


How often should I visually check my boiler?

As a rule of thumb, you should perform a visual check once a month so that you can spot any minor issues before they become big problems. You should also check your boiler if you hear any weird noises.

Which thermostat is best for boiler efficiency?

Programmable smart thermostats are the best option for boiler efficiency. You can set different heating schedules during the day and night so that your boiler is never working unnecessarily to heat your home.

How much does an oil boiler service cost?

An oil boiler service will set you back about £75 to £110. Getting your boiler serviced regularly will ensure you don’t have to pay costly repair fees down the line.

Final Thoughts

Knowing how and when to check your boiler in between its annual service dates can go a long way in maintaining your boiler and lengthening its lifespan.

If you need more tips and advice on how to check your boiler, make sure to contact Eco Happy.

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

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