No hot water? Simple checks to diagnose the problem

We’ve all been there. Stepping into the shower, shampoo in hand, only to discover that there’s no hot water! It’s a fairly common problem but, as annoying as it may be, it’s not always the fault of your teenage children, partner, or flatmate. 

Sure, in some cases, the reason why you end up getting an icy surprise when turning on your shower is because someone has already used up all the hot water, but it might also be an indication that you have a serious fault at hand.

Knowing what to do next, though, isn’t always obvious. To help you figure out why your boiler seems to be working but you don’t have any hot water, our team of boiler experts have put together a list of simple checks you can carry out before you decide it’s time to call an engineer.

How to identify if there’s a problem with your boiler

1. Check your water pressure

Low water pressure is a common problem but not necessarily a serious one. The optimum pressure for a domestic boiler is between 1 and 1.5 bar, and most models will indicate this range clearly on the pressure gauge with a green section where the needle should sit.

When you notice that your boiler’s pressure is low (i.e. when it falls below 1 bar) all you need to do is top it back up again. 

There are different ways you can repressurise your boiler depending on what brand and model of boiler you have. Generally, you will need to twist the filling loop or key. However, the newer Worcester Bosch models require you to simply pull a blue lever down. 

Unfortunately, if your water pressure levels continue to drop after you repressurise, this may indicate there’s a potential leak somewhere in your system. At this point, you'll need to get in touch with a Gas Safe registered engineer who’ll be able to come and inspect your home’s central heating system, diagnose the source of the problem, and carry out the necessary repairs.

2. Reset your boiler

Sometimes turning it off and on again really does help things. Resetting your boiler is most commonly carried out after there’s been what’s called a boiler lockout. Your boiler will perform a lockout (effectively shutting itself down to prevent any further damage) when it notices an issue within your heating system. It could be that the boiler has simply lost water pressure and needs repressurising if you have bled any radiators, for example.

But how do you reset your boiler? This will depend on your boiler’s make and model, but for modern boilers, it tends to be a button that simply reads, ‘reset’. Press and hold this button for three seconds, and then release. If you’re having difficulties with this, dig out your boiler’s instruction manual. This will explain exactly how to reset your boiler and even include diagrams so you’ll know exactly what to look for. 

If your boiler doesn’t return to normal once you’ve reset it, the best thing to do is to contact a Gas Safe registered engineer, and they’ll be able to take a further look at it. 

3. Potential frozen condensate pipe

Depending on what the weather is like outside, a frozen condensate pipe could be the reason why your hot water isn’t working. The warning signs to look out for during the winter months or after a cold snap include: 

• A weird gurgling sound coming from your boiler
• Your boiler not switching on
• No water intermittently running out of your plastic condensate pipe outside

If left untreated, a frozen condensate pipe can end up causing complete boiler failure, the condensate can back up inside the boiler and cause water damage to internal components.  This could lead to water leaks on the boiler which could cause property damage inside your house.

The condensate pipe is a white pipe that’s sometimes located outside your property and should always lead into a drain or soak away. If you do notice that your condensate pipe is frozen, you should fill up a jug with warm water (not boiling) and pour it over the condensate pipe. If you don’t feel comfortable doing this, contact an engineer to come and help.

Once your condensate pipe has been thoroughly defrosted, the condensation from your boiler will now be able to flow freely to the drain or soakaway. You should then look at insulating the pipe or even contacting an engineer to upgrade the size of to prevent it happening again 

For more information on this, read our full guide on condensate pipes and follow our step-by-step instructions on how to fix them when frozen.

4. Check for fault codes

At first glance, a fault code (or error code) can look quite intimidating. To the untrained eye, they’re a combination of numbers and letters thrown together at random, signaling that there is a problem somewhere inside your boiler. 

If you notice a fault code, don’t panic! In some cases, fault codes aren’t the end of the world (or the end of your boiler’s lifespan), and can be resolved with quick and easy DIY fixes. If you are unsure of what they mean or how to resolve them, always contact a Gas Safe registered engineer to investigate the issue further. Remember, you're not qualified to work on gas-burning appliances.

To help you identify what the problem might be, here are some of the most common fault codes for different types* of boilers.

No hot water from your Baxi boiler? Check to see if one of these faults is the cause:

Model	Code	Cause / Possible fix
GA Range	E117	System pressure too high (more than 2.9 bar). Pressure needs to be released, if the problem persists, call a Gas Safe Engineer.
GA Range	E118	System pressure too low (less than 0.5 bar). Increase the pressure to 1-1.5 bar. If the pressure keeps falling, contact an engineer
GA Range	E125	This means there’s a circulation fault in the system and that water isn’t moving from the boiler to the radiators properly. Check the water pressure is correct and then call an engineer.
GA Range	E133	Ignition fault - make sure your gas supply is working correctly and then try turning the selector to switch to rest, holding it for five seconds. If this doesn’t work, you will need to contact an engineer.

No hot water from your Ideal boiler? Check to see if one of these faults is the cause:

Model	Code	Cause / Possible fix
Logic Combi	L9 / H9 / HA / LA	Overheating - try bleeding your radiators to reduce the system pressure or, if this doesn’t work, contact a Gas Safe engineer.
Logic Combi	FD	No water flow - this could be due to low pressure, but may also be the result of internal blockages or leaks. Try repressurising your boiler and, if this doesn’t fix it, contact an engineer.
Logic Combi	F1	Low water pressure - try repressurising your boiler by adding more water into the system using the built-in filling loop.
Logic Combi	F2	Flame loss - if your other gas appliances are working, try resetting your boiler. If none of your gas appliances are working, the issue may be due to a more serious issue with your home’s gas supply, flue pipe, or faulty valves. You’ll need to contact a Gas Safe engineer to address these.

No hot water from your Navien boiler? Check to see if one of these faults is the cause:

Model	Code	Cause / Possible fix
Combi and System	003	Ignition failure - a manual reset is needed.
Combi and System	012	Flame loss - manually reset the boiler.
Combi and System	016 / 046	Heat exchanger overheated - try manually resetting the boiler if it doesn’t auto-reset.
Combi and System	594	The EEPROM (PCB) isn’t working properly - you’ll need to contact an electrical engineer to get this sorted.

An added bonus with Navien boilers is that the error codes are the same across pretty much every model in the range, so you don’t have to worry about searching to find the correct codes for your specific type of boiler.

No hot water from your Vaillant boiler? Check to see if one of these faults is the cause:

Model	Code	Cause / Possible fix
EcoTEC Pro/EcoTEC Plus	F22	Safety switch off due to low pressure. Try to increase the boiler’s pressure to 1-1.5 bar, if the pressure continues to drop after being topped up, call an engineer.
EcoTEC Pro/EcoTEC Plus	F28	Failure during start up or ignition has been unsuccessful.
EcoTEC Pro/EcoTEC Plus	F61	This is a broken gas valve, which could be dangerous. Call an engineer to fix the problem as soon as possible.
EcoTEC Pro/EcoTEC Plus	F75	No pressure change is observed, this could be due to a problem with the boiler’s pump or pressure sensor - contact a Gas Safe engineer.

No hot water from your Viessmann boiler? Check to see if one of these faults is the cause:

Model	Code	Cause / Possible fix
All Viessmann boilers	58, F6, F9, F-E1, FE-2 or F-F6	Burner in fault mode/emergency operation - possible plug-in connection problem. Reset the boiler and then call a Gas Safe engineer if the problem persists.
Vitodens 222F	A4	Air lock in the internal circulation pump or the minimum flow rate has not been achieved. Call a Gas Safe engineer.
Vitodens 100-W	OC	Insufficient power supply. Review other appliances to see if there has been a power cut, if not, you may need to call a Gas Safe engineer or electrician.
Vitodens 200-W / 222-F / Vitotronic 300 / 200/ 200-H / 050/200-H / 300-K / vitocontrol-S	10	A short circuit is causing the boiler to operate as though the outdoor temperature is 0°C. Reset the boiler and call a Gas Safe engineer.

No hot water from your Worcester Bosch boiler? Check to see if one of these faults is the cause:

Model	Code	Cause / Possible fix
CDi Compact / Greenstar 25/30 Si Combi / Greenstar 27/30 I system	C6 215	Fan speed error - try resetting your boiler to bring the fan speed back down to normal.
CDi Compact / Greenstar 25/30 Si Combi / Greenstar 27/30 I system	9A 362	Defective or incorrect heat control module (HCM) - you’ll need to contact an engineer to come and inspect your boiler and establish whether the HCM is broken.
CDi Compact / Greenstar 25/30 Si Combi / Greenstar 27/30 I system	EA 227	No flame signal due to a blockage or internal leak - a blockage could be caused by a frozen condensate pipe whilst a leak may be due to a broken gas valve or ignition lead.
Greenstar 8000	1017 W	Low water pressure - try adding more water into your boiler’s system via the filling loop. If the pressure continues to drop after this, you’ll need to call an engineer.

*Note that each brand and type of boiler will have unique fault codes, so it’s always best to consult the manufacturer’s handbook before diagnosing the problem.

Still having trouble? Don’t panic! Check out our dedicated guides for more detailed information on Worcester Bosch and Ideal fault codes.

5. Check your pilot light hasn’t blown out

If you own an older non-condensing boiler, the pilot flame could have gone out. The pilot light is a small flame that needs to be kept alight to serve as an ignition source for the main burner on older appliances. If you own a newer boiler this would not be an issue for you. One of the problems with pilot lights is that they could be blown out or go out if dirt covers the pilot burner or the injector becomes blocked. So, if your boiler has a pilot light and your heating and hot water supply have stopped, make sure it’s lit.

6. Check your programmer settings

If you have a standard boiler or system boiler, it may seem like an obvious thing to mention, but your boiler may not have turned on if your time programmer settings are incorrect or if you have turned it off by mistake. 

Always check this, along with the time, if the clocks have changed for example. Also, check that someone you live with hasn’t changed the on and off times for your boiler to heat your hot water. Once you have completed these basic checks and rectified any of the above, hopefully, the water in your hot water cylinder will start to heat. If you are still experiencing difficulties, call a Gas Safe registered engineer to investigate further. 

Remember, if you have a combination boiler, none of the above is relevant, as this type of boiler heats the water instantaneously on demand.

Still struggling for hot water?

If you’re still struggling with hot water, it’s time to seek professional advice from a Gas Safe engineer. For reliable and expert help, book a boiler repair online. Continuing issues with heating water may mean it’s time for a new boiler.