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How to prepare your boiler for winter: checklist before turning it on for the first time

Before you switch on your heating for the first time, visually inspect the boiler, check the pressure, clear the ventilation grilles, check the thermostat and bleed the radiators. However, never open the boiler or tamper with any of its internal components, as these are tasks that should only be carried out by an authorised professional.

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Checklist before you switch on your boiler

What to check?
 		Make sure that...
 		Can you do it yourself?
Exterior condition.
 		There are no water leaks or visible damage.
 		Yes.
Ventilación.
 		Que las rejillas están libres.
 		Yes.
Presión de agua.
 		Que está en los valores indicados por el fabricante.
 		Yes.
Radiadores.
 		Que los mandos funcionan y purgar el aire.
 		Yes.
Modo de funcionamiento.
 		Que está en modo calefacción, o calefacción y agua caliente.
 		Yes.
Termostato.
 		Que funcionan el encendido, el apagado y la programación.
 		Yes.
Interior de la caldera.
 		El estado del quemador, la cámara y los electrodos.
 		No.
Circuito de gas.
 		La posible necesidad de reparaciones o ajustes internos.
 		No.
Evacuación de humos. La posible necesidad de desmontaje o reparación.
 		No.

1. How to carry out a visual inspection of the outside of your boiler

An error message on the boiler display is an obvious warning sign. But even a small trace of moisture on the floor beneath the appliance could indicate that something is about to go wrong. That is why carrying out an initial visual inspection can help you prevent potential faults in your heating system. What should you look for during this inspection?

  • Signs of moisture on or around the boiler.
  • Potential drips from the pipework.
  • Signs of corrosion, rust or damage.
  • Damaged or poorly connected power cables.
  • Problems with or damage to the on/off switch.
  • Error messages on the display.

 

2. How to check and prepare the ventilation grilles

As well as being a mandatory safety feature, ventilation grilles help prevent toxic gases from building up inside your home.

Ideally, the grilles should be kept clean and unobstructed throughout the year, but the start of the heating season is a good time to carry out the three most important checks:

  • Make sure the grilles are not blocked.
  • Ensure no dirt has built up between the slats.
  • Make sure there is no furniture or objects placed in front of them.

 

3. How to check your boiler pressure

The boiler pressure is checked using a small pressure gauge, usually located on the front or underside of the appliance. In most cases, when the heating is switched off, the needle should read between 1 and 1.5 for the system to operate normally. However, it is important to check your boiler's instruction manual to find out the pressure recommended by the manufacturer.

What happens if your boiler pressure is too low or too high?

If the pressure is too low, the water flowing from the boiler to the radiators will not have enough pressure to reach them all. As a result, some parts of the house may remain cold even when the heating is on.

At the other extreme, if the pressure is too high, all system components are subjected to more pressure than they should be. If pressure remains high, it can damage the pipes and radiator valves and may even cause the boiler to shut down as a safety measure.

How can you increase the pressure in the heating system?

First, check the boiler's instruction manual to find out where the pressure valve is located. Once you have located it, turn it carefully until you hear water flowing. When the pressure gauge shows that the pressure has reached the desired level, close the valve again.

If the pressure repeatedly drops after you have adjusted it, there may be a leak in the system or a fault with the sensors. In this case, contact the technical support service.

How can you reduce the pressure in the heating system?

As a general rule, it is worth knowing that the valve used to increase the pressure cannot also be used to reduce it. Therefore, if the pressure gauge is above the correct values, there are three possible solutions:

  1. Check whether the instruction manual explains how you can reduce the system pressure yourself.
  2. If not, try draining some water from the radiator closest to the boiler until the pressure gauge returns to the recommended level. To do this, you can follow the advice on bleeding radiators in this article on our blog.
  3. If neither of the above methods works, contact the technical support service for instructions or to arrange a visit from a professional.

 

How to check your radiators before you switch on the heating

Once you have confirmed that the system pressure is sufficient for heat to reach every radiator, it is time to check their condition. Check that:

  • The valves open and close properly without having to force them.
  • There are no water leaks or damp marks on the walls or floor.
  • There is no furniture or other objects placed in front of them that could obstruct the flow of heat.
  • There are no delicate fabrics or flammable materials next to them.
  • No air has built up inside them over the summer.

How can you tell if a radiator has air in it, and how does this affect your heating?

When radiators have been inactive for months, some air can seep into the system. This air takes the place of some of the water that should be in the system, preventing the radiator from heating normally. For this reason, it is advisable to bleed all your radiators as part of your preparations for the winter season.

These are the signs that could indicate the presence of air:

  • You hear water or dripping noises coming from inside the radiator.
  • The top of the radiator is cooler.
  • Your home heats up unevenly or more slowly than usual.

Why is it better to bleed radiators with the heating switched off?

There are two reasons why it is recommended to bleed radiators when they're cold:

  1. If you do it while the heating is on, the water in the system will be above 50°C, and you could burn yourself if any water splashes out.
  2. When the heating is switched off, the water is at rest, so the air remains at the top of the radiator, where it is easier to bleed.

Why should you check the boiler pressure again after bleeding the radiators?

When you remove the air from each radiator, you also lose some of the water in the system. This small amount, multiplied by the number of radiators in your home, causes the overall system pressure to drop. That is why it is a good idea to check the boiler's pressure gauge again after bleeding the radiators to make sure that it remains within the recommended levels.

 

How to ensure your thermostat is working properly

We sometimes forget that the thermostat is also part of our heating system, and a lack of maintenance or a minor fault can make us think that the boiler is faulty when it is not. To make sure the device will function as expected, check these five points:

  • It is set to the right mode or function to activate the boiler.
  • The battery or replaceable batteries are in good condition.
  • The date and time are correct.
  • The programming feature works properly.
  • The heating reaches the temperature set on the thermostat.

 

How to switch on your boiler for the first time after summer

Once you have completed all the checks, switching on the heating for the first time will confirm that it is ready for the winter:

  1. Activate 'heating' or 'heating and hot water' mode.
  2. Turn up the thermostat to check whether the boiler starts up.
  3. Leave the system running for a few minutes while keeping an eye on it.

 

What to check during the first 15 to 30 minutes of heating

When you start using the boiler again, it is not unusual for some things to take a little while to work properly. Paying attention during the first few minutes will allow you to make sure everything is in order:

  • The boiler should start up and remain on without displaying any errors.
  • Every radiator in the house should heat up fully.
  • The house should reach the desired temperature.
  • The system should maintain a stable pressure.
  • There should be no water leaks from the boiler or radiators.
  • There should be no unusual noises anywhere in the system.
  • No unusual smells should appear.

The following table highlights some possible signs of a malfunction and what to do if they occur: 

Situation:
 		What to do:
Slight initial noise from the system.
 		Check whether it persists or disappears.
Loud or unusual noises.
 		Request a technical inspection.
The radiator is cold at the top.
 		It may need bleeding.
Pressure temporarily low.
 		Check the instruction manual.
Pressure repeatedly drops.
 		Request technical support.
An error appears on the display.
 		Check the manual or contact technical support.
A water leak occurs.
 		Switch off the boiler and contact support.
Switch off the boiler and contact support.
 		Request a technical inspection.
You notice a gas smell.
 		Continue reading this article.

What should you do if you smell gas when you switch on the boiler?

If you notice a gas smell when using the boiler, take the following measures immediately:

  1. Make sure there are no sources of ignition, such as lit candles, cigarettes or kitchen hobs.
  2. Do not switch any electrical switches on or off.
  3. Do not use your mobile phone near the boiler.
  4. Ventilate the home by opening doors and windows.
  5. Turn off the main gas supply valve, provided you can do so safely.
  6. If the smell is strong, leave the building.
  7. Call your company's emergency service and, if necessary, dial 112.

 

What NOT to do when preparing your boiler for winter

Some boiler maintenance tasks should be left to qualified technicians to avoid putting the appliance at risk and, most importantly, compromising your safety:

  1. Never open or dismantle the boiler.
  2. Never tamper with the burner or combustion chamber.
  3. Never adjust any components of the gas circuit.
  4. Never dismantle the flue gas pipes.
  5. Never attempt to fix error codes without understanding what they mean and how to resolve them.

 

Remember: preparing your boiler does not replace the mandatory periodic inspection

In this article, we have outlined a series of recommendations for getting your heating system ready for winter. However, these basic home checks, most of which you can carry out yourself, are not equivalent to or a substitute for the boiler's mandatory periodic inspection, which must be carried out by an authorised technician.

Only this comprehensive maintenance inspection, including the internal components that only a professional should access, really guarantees that your boiler is working properly and safely.  

How often should a gas boiler be serviced?

How often your boiler needs a periodic service depends on the type of boiler you have, the manufacturer's specifications and any specific regulations that may apply where you live.

As a general rule, the Thermal Installations in Buildings Regulations (RITE) mandates a two-year interval for servicing wall-mounted gas boilers of up to 70 kW, which are the most common type. However, this interval may be shorter if required by your regional government.

 

A periodic boiler inspection and a gas safety inspection are not the same thing

This situation comes up frequently: your boiler has successfully passed its mandatory periodic inspection, and some time later you receive a notification telling you that your gas installation is due for its mandatory inspection. Aren't they the same thing?

In fact, they aren't. Both involve inspections, and both have a mandatory frequency (every five years in the case of the gas inspection). However, there are three basic differences between them: 

Boiler inspection/maintenance:
 		Gas installation inspection:
What components are inspected?
 		The heating unit.
 		The gas installation.
Who carries it out?
 		An authorised professional.
 		A gas distribution company or authorised company.
How often?
 		According to RITE, your autonomous community and the manufacturer.
 		Every five years.
Is it equivalent to the checklist you carry out yourself?
 		No No

When to call a technician to check your boiler before winter

If the start of the heating season coincides with the date scheduled for your boiler's maintenance service, leaving the job to professionals is a highly recommended option.

If not, it is advisable to arrange a professional inspection if any of the following occur:

  • The system pressure drops, even after you top it up.
  • Water leaks appear from the appliance. 
  • Persistent error messages appear on the display.
  • It takes longer than usual to heat up.
  • It makes loud or unusual noises.
  • It repeatedly switches off.
  • There are visible signs of corrosion or damage.
  • It has not been used for years and you are unsure of its condition.

Having a maintenance service, such as Endesa’s Comprehensive Gas Maintenance, makes both servicing and repairs much easier. It includes an annual inspection of the entire heating system, boiler adjustments to combine safety with energy savings, and the availability of emergency visits within less than three hours.

 

Frequently asked questions before you switch on your heating

What pressure should the boiler read before you switch it on?

It depends on what the manufacturer's manual specifies. As a general guide, the correct pressure for many domestic boilers is between 1 and 1.5 bar when the heating is switched off.

Should you bleed the radiators before you switch on the heating?

Yes, to check that no air has built up inside them, and to release it if it has. Radiators should preferably be bled with the heating switched off and the radiators cold.

Do you need to bleed all your radiators every year?

It is not essential, but it is recommended, especially if you hear noises coming from inside the radiators or if they heat up unevenly.

Why does the pressure drop after bleeding the radiators?

Because some of the water in the system usually escapes along with the air when you bleed the radiators. This can cause the system pressure to drop slightly.

What should you do if the boiler pressure drops again?

If this happens repeatedly, it may be due to a fault. You should request technical support to check for potential problems with the system or boiler.

Why is one radiator cold while the others are hot?

If only one radiator remains cold, it is generally because there is air trapped inside it, the opening and closing valve is not working properly, or the system pressure is too low if it is the radiator furthest from the boiler. 

What should you do if the boiler does not start?

Check that it is properly connected to the electricity supply, that you have selected 'heating' or 'heating and hot water' mode, that the pressure is correct, that the thermostat is working properly and whether an error code appears on the display. Depending on the cause, you may be able to fix the problem yourself or you may need to contact technical support.

How often should a gas boiler undergo a technical inspection?

For wall-mounted gas boilers of up to 70 kW in homes, the Thermal Installations in Buildings Regulations (RITE) mandates a maximum interval of two years, but the manufacturer's recommendations and any other local regulations should also be taken into account.

Is passing the boiler inspection the same as having the gas installation inspected?

No. A technical boiler inspection and a gas installation inspection are different requirements, each with its own deadlines, scope of actions and authorised professionals.

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