Boiler and Heating Q&A

A boiler is a central component in any property, which is why it’s important to ensure it’s working optimally. As well as providing you with heat and hot water, your boiler affects the energy efficiency and running costs of your home or commercial unit. To help you get the most out of your boiler and heating system, take a look at these top FAQs now:

1. How Long Does a Boiler Take to Heat Water?

The length of time it takes for water to be heated depends on the boiler you have installed. In the UK, there are three main types of boilers: combi; system; and heat only (sometimes known as conventional or standard boilers).

Combi boilers are designed to provide instant hot water, although, in reality, it can take around 20-30 seconds for the water to reach its hottest temperature.

A system boiler heats water and retains it in a tank, for when it’s needed. Providing the tank has hot water in it, you’ll be able to access instant hot water when you turn on a tap. However, when the tank is empty, it takes an average of 20-30 minutes for more water to be heated, depending on the boiler model you have installed.

Similarly, a heat only boiler stores hot water in a tank, ready for use whenever a tap or shower is turned on. If the tank runs out of hot water, it should only take around 20-30 minutes for fresh hot water to refill it.

Join over 500,000 members and stop overpaying for your gas and electricity now!

By ticking here, you agree we can send you occasional emails with incredibly helpful money saving tips.
Our privacy policy outlines how we use your data and where it goes. Please make sure you read it before moving ahead with the enquiry.

2. How to Drain a Combi Boiler Central Heating System?

Every boiler and heating system is different, so it’s important to check the manufacturer’s instructions before you attempt to drain the system. In general, however, you can drain a combi boiler central heating by following these steps:

1. Turn off the boiler and disconnect it from the power.

2. Allow the system to cool down.

3. Find the drainage valve on the lowest radiator in the house and attach a hose.

4. Open the valves on all other radiators.

5. Open the valve that is attached to the hose and allow the water from the system to drain.

3. How to Flush a Central Heating System Combi Boiler?

You can flush a central heating system combi boiler without removing your radiators by following these steps:

1. Turn off the heating system and allow it to cool.

2. Drain the radiators and refill the system.

3. If your system is vented, add system cleaner to the feed and expansion tank. If your system is sealed, put a cleaner cartridge into the heating system.

4. Turn heating back on and allow it to run for approx. two hours.

5. Drain and refill the system twice.

Alternatively, you can hire a ‘power flush’ tool that affixes to the system and pushes water through it at high pressure to clean the system of sludge and debris.

If you want to flush the system by taking the radiators off the wall, you can do so by:

1. Turn the heating off and allow the system to cool.

2. Lay old towels or sheets underneath the radiator to prevent damage from occurring.

3. Turn off the radiator valve and remove the cap from the covered valve on the other side of the radiator.

4. Use an adjustable spanner or wrench to close the valve.

5. Use a radiator key to bleed the radiator and release air, before closing the bleed valve.

6. How you remove the radiator from the wall will depend on the exact type of radiators you have installed. In general, however, loosen the nuts that are holding the radiator in place. Then, lift the radiator slightly and flip it upside down before unscrewing the nuts and removing it from the wall.

7. Cover each end with your hand to prevent water from leaking and carry the radiator outside.

8. Tip the water out of the radiator.

9. Attach a garden hose to the radiator and allow water to flow through, pushing out the debris inside.

10. Reattach the radiator to the wall, open the valves and bleed the radiator again to release air.

11. Repeat this process for every radiator in the property.

It should be noted that flushing the system in this way can take a significant amount of time. Even when a technician carries out this task, it’s not unusual for it to take in excess of three hours to remove all radiators and flush them. Additionally, removing the radiators can result in leaks, particularly if you are attempting to carry them outside alone. Due to this, you may prefer to arrange for an engineer to flush the system, rather than doing it yourself.

4. How to Get Air Out of Boiler Heating System?

It’s not unusual for air to build up inside a central heating system. However, it should be released to ensure it doesn’t cause rust to develop inside the radiator or affect the performance of your heating system. To remove air from your central heating and boiler system, follow these steps:

1. Turn off the heating and allow the system to cool.

2. Start with the radiator that is closest to the boiler. Place a bowl or old cloth next to the bleed tap, in case water is released.

3. Place a radiator key on the bleed tap and turn slowly in an anti-clockwise direction. You don’t need to open the valve all the way, just enough to let the air be released. You may notice a hissing sound as the air escapes. When water begins to trickle from the bleed tap, close it again using the radiator key.

4. Repeat this process on all radiators in the property, starting from the lower floors and moving upwards.

5. Once complete, turn the boiler back on and check the pressure. If necessary, repressurise the system.

Although a radiator key should be used to bleed a radiator, most bleed valves can be adjusted using a standard flathead screwdriver too.

5. How To Set Heating Timer on Vaillant Boiler?

The exact process of setting the heater timer will depend on which Vaillant boiler or thermostat model you have installed. For digital Vaillant thermostats, however, you can set the heating timer so that the heating comes on and turns off at set times throughout the day. To do this, press the Menu button on the thermostat (this is usually the left-hand control button) and scroll down to ‘Time Programmes’. Press Select (usually the right-hand control button).

Following this, you’ll see a day specified on the display, along with three timer options. This allows you to set three different timers throughout the day, along with three different temperatures. Simply use the controls to confirm when you would like your heating to come on and switch off, along with the desired temperature and press the right-hand control button to save, when prompted.

6. What Is a Heat Only Boiler?

A heat only boiler requires two water tanks (usually situated in the loft) and a hot water storage cylinder in order for the system to work. A cold water tank is filled with water from the mains before being heated in the hot water tank. A feed and expansion tank is used to top up the water level in the central heating system, as required, Water is also fed down to the boiler, where it is heated via a heat exchanger for use in the central heating system. A pump then transported this water to the hot water cylinder, before being sent to the radiators when the heating system is turned on.

Although heat only boilers are a fairly traditional option, they can be suitable for use in larger homes or commercial units. When the heating and hot water are going to be in use at the same time or when

multiple taps or showers are going to be used at once, for example, a heat only boiler system is capable of meeting these demands without it having a negative impact on the performance of the system.

7. What Should Boiler Pressure Be When Heating Is Off?

When the heating is off, the pressure on your boiler display should read between 0.5 – 1 bar. If the pressure is below 0.5 or above 2 bars when the heating is off, it’s likely your system needs to be repressurised.

8. What Should Boiler Pressure Be When Heating Is On?

When your central heating system is switched on, the pressure should typically be between 1 – 1.5 bar. If it is below 1 or above 1.5 bar, there’s a good chance the system needs to be repressurised.

Although it’s possible to adjust the settings on your thermostat, flush the heating system or repressurise it yourself, you should only undertake these jobs if you feel confident enough to do so. Furthermore, there are some tasks that should only be undertaken by a qualified engineer, so be sure to read your owner’s manual before you adjust the settings or begin working on your central heating system.