No hot water is one of life’s most frustrating surprises. Whether you’ve jumped in the shower and been hit with cold water, or noticed your radiators aren’t warming up, the cause isn’t always as serious as it seems. Before you call out an emergency plumber, it’s worth spending five to ten minutes running through a few basic checks yourself. You might find the fix is simpler than you think, and it could save you a call-out fee.
Most UK homes run on a combi boiler, usually tucked away in a kitchen cupboard or an upstairs airing cupboard. Here’s what to look at.
Is Your Boiler Working?
Start by locating your boiler and checking it’s actually running. Look for a status light or digital display. If it’s blank or showing an error code, your boiler may have locked out and need a reset. Hold the reset button for 3 to 5 seconds. If it fires up and then locks out again shortly after, don’t keep resetting it as this points to an underlying fault that needs a professional. Also, check that the boiler controls haven’t been accidentally adjusted. If you store things in your airing cupboard, items can knock the dials without you realising.
Is Your Thermostat Set Correctly?
This is one of the most common and easily missed causes of a hot water outage. Check your thermostat or programmer and make sure the hot water hasn’t been switched to off or timed only. Also check that the programmed schedule is correct, as a power cut can reset your clock and cause the boiler to fire at the wrong times or not at all. If you use a smart thermostat like Nest or Hive, check the app to confirm your schedule is still active.
Is Your Boiler Pressure Correct?
Pressurised boilers, which are standard in most modern homes, won’t operate if the pressure drops too low. Find the pressure gauge on your boiler and check it reads between 1 and 1.5 bar when the heating is off. If it’s below 1 bar, you’ll need to repressurise the system.
How to Repressurise Your Boiler
Repressurising a boiler sounds technical but is something most homeowners can do safely in a few minutes. Here’s how:
Turn the boiler off and let it cool down completely.
Find the filling loop, which is usually a braided silver hose with a valve at either end, located underneath the boiler.
Open both valves slowly until you can hear water entering the system.
Watch the pressure gauge and close both valves as soon as it reaches 1.2 bar.
Turn the boiler back on and press reset if needed.
If your boiler regularly loses pressure, this is a sign of a leak somewhere in the system and you should book a service rather than keep topping it up.
Is Your Gas Supply Consistent?
If your other gas appliances such as your hob or gas fire aren’t working either, the issue may not be your boiler at all. Local utility works can sometimes interrupt gas supply temporarily. Check with a neighbour or contact your gas supplier to rule this out. You can also call the National Gas Emergency line on 0800 111 999 if you suspect a more serious supply issue.
Why Do I Have Heating But No Hot Water?
This is a very common complaint in homes with a combi boiler, and the most likely culprit is a faulty diverter valve. The diverter valve is responsible for directing hot water either to your taps or to your radiators depending on demand. When it gets stuck or wears out, it often defaults to heating only, leaving you with warm radiators but cold taps. This is not something you can fix yourself and will need a Gas Safe registered engineer to replace.
Common Boiler Error Codes and What They Mean
If your boiler display is showing a fault code, don’t panic. Here are some of the most common ones and what they typically indicate:
Worcester Bosch
EA 338 usually indicates a failed ignition. E9 points to an overheat, and D5 relates to the flue or ventilation.
Vaillant
F22 means low water pressure. F28 and F29 both relate to ignition failure. F75 indicates a fault with the pressure sensor or pump.
Ideal
F1 means low pressure. F2 indicates the boiler has overheated. L1 points to an ignition fault.
Your boiler manual will have a full list of codes specific to your model. If you can’t find it, most manufacturers have their manuals available to download on their websites.
Combi Boiler vs System Boiler: Does It Make a Difference?
Yes, the type of boiler you have affects where you look first.
With a combi boiler, hot water is produced on demand directly from the mains. There is no hot water cylinder, so if you have no hot water it is almost always a boiler issue rather than a storage issue.
With a system boiler, hot water is stored in a cylinder. If you have no hot water but your heating is working fine, the problem may be with the cylinder itself, the immersion heater, or the motorised valve that controls flow to the cylinder rather than the boiler. Check whether the cylinder feels warm to the touch. If it’s cold, the issue is likely with the hot water circuit rather than the boiler.
Frequently Asked Questions
Why does my boiler keep losing pressure?
Recurring pressure loss usually means there is a small leak somewhere in the system, either at a radiator valve, a pipe joint, or within the boiler itself. It can also be caused by a faulty pressure relief valve. A heating engineer can carry out a leak detection check to find the source.
How long should it take to get hot water after a boiler reset?
With a combi boiler, hot water should be available almost immediately after the boiler fires successfully. With a system boiler and cylinder, it can take 30 to 60 minutes for the stored water to heat up fully.
Can I use my boiler if the pressure is too high?
If the pressure is above 2.5 bar, your boiler may shut itself off as a safety measure. You should not keep overriding it. High pressure can be released by bleeding a radiator slightly, but if it keeps rising you should call an engineer as the pressure relief valve may need replacing.
Why do I have no hot water in the morning but it works later in the day?
This is often a thermostat or programmer issue. Your boiler may not be scheduled to heat water early enough in the morning. Check your programmer settings and add an earlier heating slot. If the schedule looks correct, it could point to a slow-filling cylinder or a fault with the diverter valve.
Is it safe to use my boiler if it keeps cutting out?
You should not keep resetting a boiler that repeatedly locks out. This is the boiler protecting itself from a fault, and continuing to override it could cause damage or, in rare cases, a safety risk. Book a service as soon as possible.
When to Call a Heating Engineer
If you’ve worked through all of the above and still have no hot water, it’s time to call a Gas Safe-registered heating engineer. There may be a fault with an internal component, such as the diverter valve, heat exchanger, pump, or pressure sensor, and these need a qualified professional to diagnose and fix them safely.
L&P Heating Services covers Bristol, Bath, and Somerset. Our engineers are Gas Safe registered and available for boiler repairs and emergency call-outs. Call us on 01275 400 687 or send us a message, and we’ll get someone out to you as soon as possible.