A21 fault Worcester boiler

Worcester boiler A21 fault code – How to fix it!

If A21 appears on your Worcester boiler’s display screen or your room thermostat, it means that your heating system is experiencing an issue.

In terms of Worcester boiler error codes, the A21 error code means that your boiler and thermostat are not communicating with each other due to the lack of an RF signal. The Worcester error code A21 is the most common error and can be fixed easily without the assistance of an engineer.

Can you fix the Worcester A21 fault code or RF signal yourself?

This fault is often easily fixed by DIY without incurring excessive costs. A Gas Safe registered engineer must perform any work on the boiler or the final connection of water pipes to it. But as this is likely due to RF signal strength, then you should be able to remove this Worcester boiler error code yourself

This guide will help to explain the problem, how to fix it, and when to call an engineer to perform further repairs.

Worcester boiler wireless thermostat problems

Worcester Bosch defines this code as “Loss Of RF Signal”. Radio frequency is the way a thermostat wirelessly communicates with the boiler to tell it when to turn on. They have a temperature sensor built inside which tells the boiler how hot or cold it is in a room.

This is when your thermostat registers a lower temperature than you have set. That’s why they are often placed in the areas where you spend most of your time.

Once the temperature has been recorded, the thermostat sends an alert to its receiver partner, also known as a receiver.

This unit is typically placed near the boiler unit and relays the signal from it to the boiler. Once the controls in the room is set to the correct temperature, the boiler will turn on the heating.

When there is a RF interruption between the receiver and room thermostat, the A21 code will appear. This stops the boiler from knowing when it should turn on.

How to fix the Worcester A21 error code?

Thermostat Requires New Batteries

Like any other battery-powered appliance they will sometimes need to be recharged.

The display may have had a low battery symbol before the A21 code was introduced. This symbol means that you have 60 days to replace your battery before the thermostat stops working.

If your it was installed recently, low batteries won’t be an issue.

How to replace the batteries in a Worcester wireless thermostat

To access the thermostat’s battery compartment, you must remove the thermostat from its mounting plate.

Depending on the model, the method you use to do this will differ. The following steps are possible for most Worcester Bosch thermostat models:

  • Place a flat-bladed screwdriver in the slot below the thermostat.
  • Gently twist until it is freed from the mounting plate
  • Before replacing the batteries, remove the entire wall.
  • Reattach the thermostat by aligning the top with the wall mounting spot and pushing gently until it snaps into position

Most models will need the same process. However, if you are unable to find an opening slot on your thermostat’s manual, you might want to consult it.

The A21error code can be caused by batteries. After this is complete, you will need to program the thermostat again to your preferred settings.

Do I need a Gas Safe engineer?

Your boiler may be in an awkward place, such as your garage or attic. The receiver could be too far from the thermostat.

An engineer might move the receiver down to a better location.

A wireless thermostat may not be suitable for you if there is too much distance between the receiver and the desired area, or if structural features like steel joists are interfering with the communication.

An engineer might suggest replacing a wired thermostat in this instance. These thermostats usually cost less than £100 plus the labour costs for installation.

Thermostat Out of Range for the Receiver

It is possible that the thermostat has not been in a good position to communicate with its receiver if it was installed recently.

The thermostat records the temperature at the location it is located. This then tells the boiler whether to turn on. This function will not take place if the signal is lost or inconsistant.

Worcester Bosch believes that not all engineers agree with this assertion. However, Worcester says some buildings aren’t suitable for their wireless products.

This is especially true for modern housing, which includes steel components like rolled joists or layers within walls as well as foil-lined plasterboard.

If the Thermostat Is Out of Range of the Receiver try this:

You can test this by removing the thermostat from its mounting plate.

Take it to the boiler.

This process is used to check the signal of a Worcester boiler thermostat.

  • Do not press the menu button for longer than three seconds.
  • To select Info, turn the knob and then press the knob.
  • To select Signal strength, turn the knob and then press the knob to enter function.
  • The signal is measured from 1-10. Anything above 4 is acceptable, but anything more than 7 is better for consistency.

You can move the stat to an area that has a stronger signal by taking out the wall mounting plate.

Remember that the thermostat’s temperature will control the heating system and not the hot water.

It makes sense for most people to place it in their living room as this is where they spend most of their time. You should not place it in direct sunlight, near heat sources, or where temperatures can be affected.

Before you move the wall mounting plate, you can test the position of the thermostat by leaving it there.

When to call a gas safe engineer

A radio frequency reader is a tool that engineers can use to determine if other devices are causing interference.

They may recommend switching to a wired thermostat if it is impossible to move the thermostat or these devices.

Other radio frequency signals are interupting

It’s possible for wireless gadgets to interfere with the signal between the thermostat and the receiver if there are many of them.

Because any device that uses radiofrequency to communicate will be competing for ‘airspace’.

Fixing an Interruption of the RF Connection

It is possible to identify the device that is causing the A21 problem.

If the code is found in the evenings, when the console is turned off, it’s most likely the culprit.

It might be possible to avoid moving the thermostat. If possible, move the other device farther away or make sure it is only used when heating isn’t on.

When To Call An Engineer

Your engineer might suggest that the problem is caused by a defective component after examining all possible causes.

Sometimes parts can be replaced or repaired. If a complete replacement is needed, it is likely to be the thermostat and the receiver.

Worcester Bosch makes many models that are factory-paired, which means they cannot be paired with a different part.

This will vary depending on the model of the thermostat that you choose. More recent models can cost up to £200.

Faulty Thermostat/Receiver

It is possible that one of the parts may have broken.

Both parts are necessary for the connection to the boiler to occur, so A21 error code could indicate that one of them is damaged.

If the error code appears on the boiler’s display screen and the room thermostat’s screen remains blank, it is likely that the thermostat is defective and you will need to be replaced.

How to clear a Worcester Boiler A21 Fault

You can often clear the A21 error code off your thermostat’s screen by yourself by resetting it with the reset button. You can also try resetting your boiler too by turning the central heating temperature knob on older models. Before calling an engineer, there are several steps you can take to diagnose and repair the thermostat safely.

You can arrange for an engineer to visit you if all other options you have tried have failed.

Make sure you take advantage of any free repairs or replacements if your Worcester Bosch boiler is still within its warranty period.

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