Homeowners Professionals

What to do if your boiler is working but you have no hot water

Most UK homes rely on a gas combi boiler for both heating and hot water. As well as being effective and economical, they also have a reputation for being extremely reliable. However, as a piece of equipment that is typically in use 24 hours a day seven days a week, it is inevitable that from time to time problems may occur. One problem that can be particularly frustrating is when the heating is working but there is no hot water, or if there is hot water but the boiler is not heating your home. Read on to learn more about common causes for these problems and how to deal with them.

1. Check that you have electricity, gas and water

The first rule of solving problems with your boiler is to start with the simplest possible causes. Before checking anything else, it is important to make sure that the boiler itself is actually working. Always begin at the boiler control panel. If you have a digital display and nothing is shown, it may be that there is no power to the boiler due to a power cut. Try turning on your lights and sockets to quickly confirm or eliminate a problem with the power supply. You could also check that all the fuses in your fuse box are in the correct position.

In a similar manner, it is also important to make sure you have gas and water. These can be checked by running a tap and turning on another gas appliance such as your cooker.

If you have done all of the above and are happy that your electricity, gas and water are all working, then it is time to check for pressure issues and basic fault codes.

2.  Check boiler pressure

Low boiler pressure can cause a whole host of boiler issues, including an inability to generate hot water. On top of this, while some boilers are able to tell you pressure is low through the use of a fault code, if you have an older boiler, it’s easy for a low pressure fault to go unnoticed until the functionality of the boiler is impacted.  

Luckily, it is simple to check boiler pressure and re-pressurise it if required. If you have a Viessmann boiler, check out our step-by-step re-pressurising guide for further advice.

3.  Is there a fault code displayed?

Many boiler problems will result in a fault code being displayed in your control panel. If you have the operating manual to hand, this is the best place to look for what a fault code on your boiler means.

If you have a Viessmann boiler, you can also use the convenient online boiler fault code tool.

Remember, boiler fault codes can vary from boiler to boiler. If you can’t find a description for your fault code or if instructed by the manual, you may need to contact a Gas Safe engineer for assistance.

4.  Check the boiler controls

If you still have no hot water or no heating after checking the above steps, then you will want to check that the boiler settings are correct. Your boiler will have separate controls to turn on the heating and hot water. It is possible that the hot water or heating may have been set to off by mistake, or the setting has been inadvertently changed.  

Check the timer

Some boilers may have a timer to control the hot water. If your boiler timer controls your hot water, this may be the cause of the problem. Your timer may have been affected by the clocks changing, power supply, back-up batteries failing or even somebody altering the settings without you knowing. Adjusting your timer may resolve the problem.

Check the thermostat

Your heating temperature is usually controlled by a thermostat. For most boilers this will be a manual dial mounted on the wall in the main living area or hall. Newer boilers may be fitted with digital thermostats. Ensure that the thermostat has not been accidentally set to off. Set the thermostat to a higher temperature with the timer set to active, and see if the boiler fires up. If it fails to respond, there may be a problem with the thermostat. This will require attention from a trained engineer.

5.  Check the diverter valve

If you have eliminated any other causes listed above and you still have heating but no hot water or your boiler heating is not working but the water is, then it is likely that you have a problem with the diverter valve. This is a valve that opens and closes to provide heat to the radiators or to heat your water.

If your heating is working but you have no hot water or vice versa, it is likely to have become stuck. You will need to contact a Gas Safe engineer to solve a problem with your diverter valve.

6.  Reset the boiler

If you have tried the first five steps and your seemingly working boiler is still not providing hot water and/or heating, the final thing you can try before calling in the help of a trained specialist is resetting the boiler. Whether you're a homeowner or a tenant, knowing how to safely reset your boiler can come in handy during a range of unexpected malfunctions or error codes, including if your boiler is simply not working despite everything appearing functional.

Finding out exactly how to reset your boiler will naturally depend on the particular make and model you have. This is to say, for some models you may have to turn a dial or hold down a combination of buttons, for example. For this reason, it’s always a good idea to consult your boiler’s manual before attempting to reset. However, there are a number of common steps that nearly all boiler resets involve.  

  1. Ensure your boiler is not actively working when you attempt a reset. If your boiler is working, you will be able to tell by the presence of a flame sign on your unit’s digital display or simply by the sound of the boiler operating.
  2. Once you are sure the boiler is not operating, it’s time to locate the reset button. As mentioned above, all makes and models are different, so be sure to check your boiler’s manual to find the correct (combination of) buttons you need to press.
  3. Once you have carried out the reset procedure - as described in your boiler’s manual - you will need to wait for your boiler to restart. This might take a few minutes. Usually you will know when the restart has begun when you hear the boiler ignite and/or the digital display turns back on.
  4. Finally, following a reset, you will need to monitor the operation of your boiler for 10-15 minutes. If your boiler starts to operate normally within this time, you can be sure the reset has worked. If you encounter the same issues experienced before the reset, or if the boiler doesn't restart at all, it's best to contact a qualified heating engineer to diagnose and resolve the problem.

The boiler is working but I have no hot water or heating

If you have followed steps 1 to 6 above and you have neither hot water nor heating, it is likely that there is a fault with a component that requires attention from a trained engineer. We recommend that you have your boiler inspected as soon as possible.

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