Hot water is something we tend to take for granted and expect to be available when we need it. If you have a combi boiler, you’ll be used to having on-demand hot water, day and night, while those with a conventional or system boiler will be using hot water that’s been heated and stored in a tank for later use.

If you’ve suddenly discovered that your hot water isn’t working, there are some things you can do and check to find the root of the problem and get your hot water back again in no time. 

Things to check when you have no hot water

Is your boiler working?

When you have no hot water, the first thing to check is that your boiler is working and the pilot light is visible.

If your boiler has a fault, it will likely display as a fault code on the main screen. There will be a different code for each problem, so you should check with the manufacturer to see which error the code corresponds to. You can find a list of Viessmann’s fault codes here.

Some fault codes can be rectified yourself with a simple boiler reset, whilst others may need professional attention. If you are not sure how to fix the fault code, it is recommended that you contact a qualified engineer for advice.

Are the boiler’s settings correct?

A boiler has all kinds of settings, many of which don’t need to be adjusted or changed. But there’s a chance you or someone else could have accidentally altered the settings, so you may want to make sure that the hot water is set to a reasonable temperature. Your hot water should be set to 60 degrees, so ensure it isn’t any lower than this.

Is it programmed correctly?

Your gas boiler may be programmed to come on at a particular time, and it will also consider the temperature in the home, and may not come on if your home is too warm already. Therefore, there are a few different programming settings to check.

First, ensure that your thermostat is set to a suitable temperature. This should be anywhere between 18 and 21 degrees.

Things such as power cuts and low battery can have an impact on the timer, so you should check that the timer is set to the correct time and date, that it hasn’t run out of batteries and that it’s correctly programmed.

Finally, you should ensure that the boiler is currently programmed to both heat and provide hot water. There are some settings that mean it does just one or the other, so check that this hasn’t been incorrectly adjusted.

Is your energy supply ok?

Your boiler relies on a suitable energy supply in order to work. Not only does it need gas to burn, but it also requires a small amount of electricity to start up and to work the digital display. You can check if your energy supply is ok by testing other appliances. For example, to see if the gas supply is working, you can try turning on a gas hob or fire. To check the electricity supply, turn your lights on and off or test some plug sockets. You should also take a look at your fuse box to see if any fuses are tripped, as this could affect whether you have hot water or not.

If there is a tripped fuse, you may wish to take our suggestions above and reset the boiler’s timer and programmes.

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Is your water supply ok?

This may seem like an obvious fix, but you should also check that your home has a sufficient water supply. If you don’t have water coming from any taps, whether hot or cold, then there may be a temporary supply interruption. You could contact your provider to see if they can help you out or give you any more information, or you could wait for normal services to resume.

If you have a conventional boiler system, you may wish to check that there is water present in the cold water tank (usually located in the loft). A tank that has run dry could demonstrate problems with the ballcock, which would prevent it from refilling itself as needed. 

Do you have a frozen pipe?

Frozen pipes could be causing your hot water issues, and this can be a common problem when outside temperatures drop below freezing. The condensate pipe is the one that carries waste water vapour away from your boiler and is most likely to freeze as it has no insulation at the point where it exits the house. You will be able to see ice on it if it has frozen, and can use warm water to slowly defrost it.

The pipes within your walls are also at risk of freezing, but it can be difficult to determine when this is the case. You may notice that you have low water pressure.

Is the pressure too low?

Low boiler pressure can be a reason for your lack of hot water. When the pressure drops very low or rises too high, the boiler can turn itself off altogether for safety reasons.

The water pressure in the system should be around 1.5 bar. You will be able to see this by looking at the pressure gauge located on the front of your boiler. If the pressure is too low, you should repressurise the system by opening the filling loop to allow more water in. If the pressure is too high, you may need to bleed the system slightly to bring it back down to within the normal range.

Important: Be sure to consult the operating manual first to ensure that you are able to re-pressurise the boiler yourself. If there are no instructions for this or if you have any doubts, be sure to seek the advice of a qualified engineer.

If you continue to experience problems with your boiler losing pressure, find out more about possible causes and solutions in our advice concerning the topic boiler loses pressure.

Is there a water leak?

A leak in your heating system can cause a fall in pressure which, as we know from above, can cause your boiler to shut down.

Leaks can also cause other problems associated with damp which may lead to significant damage. Look for patches on the ceiling, peeling or flaking paint on or around pipes, swollen woodwork and mould patches.

Is there an issue with the diverter valve?

The diverter valve is the part of your heating system that allows the boiler to switch between hot water and heating, depending on where the demand is highest.

If the diverter valve is not working properly, it could be stuck in the central heating position or may have developed a fault, and either of these issues can result in a lack of hot water.

If there is a problem with the diverter valve, you’ll need to call a Gas Safe registered engineer to fix it or replace the part altogether.

Is your boiler big enough?

If you have eliminated any fault in the system and you have a recurring problem with your hot water supply, the issue may be that the boiler simply isn’t big enough and is struggling to provide enough heat and hot water for your house.

In the long term, it may be cost effective to upgrade to a larger boiler if this is the case. An expert will be able to advise you of the optimum boiler size for your home based on your current and future needs.

Still got no hot water?

If you are confident that your hot water problem is not caused by one of the above problems, then it may be advisable to seek help from a trained Gas Safe engineer.

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