Worcester Boiler No Hot Water? Causes and What to Check
Worcester Bosch boiler giving no hot water, or heating but no hot water? The settings and supply checks to try first, the common combi and cylinder faults behind it, and when you need a Gas Safe engineer.
If your Worcester Bosch boiler gives no hot water, first look at the display for a fault code or flashing light, check the hot water setting has not been turned down or switched off, and check the pressure gauge. On a combi, open a hot tap fully: the boiler needs a minimum flow to fire, so a trickle from a scaled tap or low mains pressure may not be enough. If the heating works but the hot water does not, the usual culprits on a combi are the diverter valve or the hot water flow sensor. With a cylinder, check the programmer, cylinder thermostat and motorised valve. Anything inside the boiler needs a Gas Safe engineer.
Key Takeaways
- Check the display first: a code or flashing light changes what you should do next.
- Hot water turned down, switched off or on a timer is the most common easy fix.
- Combis need a minimum flow before they fire, so low water pressure can look like a boiler fault.
- Heating working with no hot water on a combi usually points to the diverter valve or flow sensor.
- On cylinder systems, the fault may be the programmer, cylinder stat or motorised valve rather than the boiler.
- Leave anything behind the casing to a Gas Safe engineer.
If your Worcester Bosch boiler is giving no hot water, check three things before anything else: whether the display shows a fault code or flashing light, whether the hot water setting has been turned down, switched off or put on a timer, and whether the pressure gauge is in range. On a combi, also open a hot tap fully, because the boiler needs a minimum flow of water before it will fire. If the settings are right and the heating still works, the fault is usually the diverter valve or the hot water flow sensor on a combi, or the programmer, cylinder thermostat or motorised valve on a cylinder system. Those need an engineer.
Check the display first
A code on the display, or a flashing blue light or reset button, means the boiler has locked out. In that case you have no hot water and usually no heating either, and the cause is the lockout, not the hot water side.
- Write down or photograph the full code, including the three-digit number. Worcester's Greenstar CDi Compact instructions ask you to quote both parts when reporting a fault.
- If it shows EA 227, the boiler could not light. Our Worcester EA 227 guide covers the gas, meter and condensate pipe checks.
- If there is no screen but a light is flashing, our guide to a Worcester boiler flashing blue light explains what that means on different models.
If the display is normal and the heating works, carry on with the checks below.
Five checks you can do
Hot water setting
Check the hot water temperature control on the boiler has not been knocked right down or switched off. On a combi, turning it up slightly and running a tap will tell you quickly whether the boiler responds.
Timer and programmer
With a cylinder, the hot water only heats when the programmer calls for it. Check the clock is correct after a power cut or the clocks changing, and try the boost or "on" setting.
Pressure gauge
Most sealed systems sit around 1 to 1.5 bar when cold. If it is well below, repressurise the boiler as your manual describes and reset once if a code is showing.
Tap flow
Open the hot tap fully. A combi fires when it senses water flowing, so a half-open tap, a scaled aerator or a weak mains supply may not be enough. Try the kitchen tap, which usually has the best flow.
One tap or all of them?
If only one tap or shower runs cold, the fault is at that outlet, not the boiler. A shower mixer with a failing cartridge is a common example, covered in our guide to no hot water in the shower.
If every cold tap in the house is also weak, the problem is the incoming supply. Our guide to low water pressure shows how to test it with a jug.
Combi: heating works but no hot water
A Worcester combi heats water on demand. When you open a hot tap, a flow sensor detects the water moving and tells the boiler to switch from heating to hot water. A diverter valve then sends the hot water from the boiler through a plate heat exchanger that heats the water going to your tap. If any of these parts fail, the heating can keep working normally while the taps run cold.
| Part | What goes wrong | What you might notice |
|---|---|---|
| Diverter valve | Sticks on the heating side, so hot water never gets priority | Radiators get hot when you run a hot tap |
| Flow sensor | Does not detect the tap opening, so the boiler never fires for hot water | Boiler stays silent when a tap is fully open |
| Plate heat exchanger | Scale from hard water blocks it and cuts the heat transfer | Hot water starts warm then fades, or goes hot and cold |
| Hot water sensor | Gives a wrong reading, so the boiler switches off early | Water swings between hot and cold |
London's hard water makes scaling a real factor on older combis. If the boiler has never had a scale inhibitor fitted, mention that to the engineer. We explain the diverter valve in more detail, along with the equivalent faults on other brands, in our guide to no hot water but the heating works.
System and regular boilers with a cylinder
If your Worcester boiler heats a hot water cylinder, it can be working perfectly and the hot water can still be cold because nothing is asking it to heat the cylinder. Work through the controls in order.
- Programmer. Is the hot water channel on? Try boost.
- Cylinder thermostat. This is the dial strapped to the side of the cylinder. If it is turned too low, the cylinder never calls for heat.
- Motorised valve. Near the cylinder there is usually a valve with an electric head that opens to let boiler water into the cylinder coil. If it sticks shut, the boiler fires for heating only.
- Immersion heater. If you have one, switching it on is a useful temporary way to get hot water and tells you the cylinder itself is fine. Our guide to an immersion heater not working covers that side.
If the pipe going into the cylinder coil stays cold when the programmer is calling for hot water and the boiler is running, the motorised valve is the likely fault. That is a job for an engineer, as the valve is wired into the heating controls.
Hot water that is only lukewarm
On many Worcester combis the ECO setting switches off the preheat, so the boiler does not keep its hot water side warm between uses. Hot water then takes a little longer to come through, which some people mistake for a fault. If the water never gets properly hot, though, even after running for a minute, the usual causes are a scaled plate heat exchanger, a partly stuck diverter valve or a temperature setting that is too low.
If you have a cylinder and the hot water runs out quickly rather than being cold from the start, see our guide to hot water running out quickly.
When to call an engineer
Call a Gas Safe registered engineer when the settings are right, the pressure is in range, the taps have good flow and you still have no hot water, or when a code keeps returning after one reset. An engineer will test the flow sensor and diverter valve, check the plate heat exchanger for scale and, on a cylinder system, test the motorised valve and thermostat wiring.
If your boiler is still under Worcester's guarantee, check the terms before booking a repair, as the manufacturer may need to arrange it. If you rent, tell your landlord or agent in writing. Hot water is part of the landlord's repairing obligation, and they may already have an engineer or cover in place.
No hot water from your Worcester?
Tell us the model, any code and whether the heating still works. Our labour is £95 an hour and the £60 call-out is waived on jobs over two hours. We confirm the price before any work starts.
📞 Call 020 7870 3200More on our no hot water repairs and boiler repair service.
Frequently Asked Questions
Why is my Worcester boiler not giving hot water but the heating works?
On a Worcester combi, heating with no hot water usually means the diverter valve is stuck on the heating side, or the flow sensor is not detecting that a hot tap is open. On a system or regular boiler with a cylinder, it usually means the programmer, cylinder thermostat or hot water motorised valve is not calling for heat. Both need an engineer if the settings are correct.
How do I reset my Worcester boiler for hot water?
If the display shows a fault or the light is flashing, reset the boiler once using the reset button as your model's instructions describe. On the Greenstar i Junior, for example, the instructions say to hold it for about five seconds. A reset will not fix a mechanical fault such as a stuck diverter valve, so if there is no code, check the settings instead.
Can low water pressure stop a Worcester combi giving hot water?
Yes. A combi only fires for hot water when it detects enough flow through the hot water side. If the mains pressure is low, a tap filter or aerator is scaled up, or the tap is only opened slightly, the boiler may not fire. Open the tap fully and check other taps. If all cold taps are weak too, the problem is the supply.
What does the ECO button do on a Worcester boiler?
On many Worcester combis the ECO setting switches off the preheat, so the boiler does not keep its hot water side warm between uses. It saves gas but means hot water takes a little longer to come through. It does not stop the boiler producing hot water altogether.
Is no hot water an emergency?
It is not usually dangerous, but it can be urgent in a home with young children, elderly or unwell people. If you smell gas or a carbon monoxide alarm sounds, turn the boiler off, leave the property and call 0800 111 999. Otherwise, check the basics and book a repair.
Sources and further reading
Source links checked 27 September 2026. Scheme rules and manufacturer instructions can change; use the current official guidance for your account or exact appliance.