Why is my Worcester boiler not giving hot water?
A Worcester boiler stops giving hot water for one of three reasons: the boiler is not firing at all, it is firing but sending the heat to the radiators instead of the taps, or it is not detecting that you have opened a tap. What else is happening tells you which one you have.
On a Greenstar combi the same burner heats both the radiators and the hot water. A diverter valve inside the boiler switches the heat between them, and a flow sensor on the cold water inlet tells the boiler when a hot tap is running. If either of those parts fails, the heating can work perfectly while the taps run cold.
| What you notice | Likely cause | What to do |
|---|---|---|
| No hot water and no heating, code on the display | Lockout, low pressure or no gas | Look up the code, check the pressure and gas, then reset once |
| Heating works, boiler stays silent when you run a hot tap | Flow sensor not detecting flow, or very low mains flow | Check other cold taps and the stopcock, then call an engineer |
| Boiler fires when you run a hot tap but the water stays cold, radiators warm up | Diverter valve stuck in the heating position | Gas Safe registered engineer |
| Hot water takes longer than usual to arrive but does come | Eco mode on, preheat off | Switch to preheat if you prefer faster hot water |
| Hot water arrives but is only warm | Temperature set low, tap flow too high or scale | Check the setting and the tap flow |
| System boiler with a cylinder, no hot water | Programmer or cylinder thermostat | Check the hot water channel and cylinder thermostat |
Check the hot water setting on your Greenstar
Start with the boiler's own hot water control, because it is easy to knock or change without noticing. Where it sits depends on the model.
- Greenstar i. The user instructions list separate hot water increase and decrease buttons on the control panel. Press them to see and change the hot water temperature on the display.
- Greenstar Si and CDi display models. These have a hot water temperature control knob on the front panel. Turn it to the setting you want.
- Greenstar 4000. The user instructions say to press the hot water key to show the set temperature, then use the arrow keys to change it.
- Greenstar 8000 Life. The user instructions say to press the hot water key, then adjust the temperature between 35 and 60 °C. The new setting saves after five seconds or when you press OK.
If the setting is at its lowest, raise it and run a hot tap again. The Greenstar i fault finding table lists a hot water temperature set too low as the first cause of water that is not hot enough.
Eco mode and preheat
Many Greenstar combis have an eco button or an eco and preheat setting. In preheat mode, the boiler keeps its hot water heat exchanger warm so hot water reaches the tap sooner. Eco mode switches preheat off to save energy, so you wait a little longer at the tap. The Greenstar i and 4000 user instructions both describe it this way, and on the 4000 eco is the default setting.
Eco mode never stops hot water altogether. If it has been switched on recently, you may simply be turning the tap off before the hot water arrives. Run the tap for a minute before deciding there is a fault.
Check for a code and the pressure
If there is no heating either, the boiler is probably not firing, and the display usually says why. A combi that has locked out gives no hot water, because the same burner serves both jobs.
- Low pressure. With the system cold the gauge or display should read 1 to 1.5 bar. A low pressure code such as CE 207 stops the boiler until it is topped up. Our Worcester boiler pressure guide shows how on each Greenstar.
- No flame. EA 227 means the boiler tried to light and could not detect a flame. Check the gas supply and prepayment meter credit.
- Other codes. A code such as D5 also stops the burner. Look up any code on our Worcester error codes page before resetting.
The Greenstar i fault finding table also lists air or low pressure in the system as a cause of poor hot water, and gives bleeding the radiators and repressurising as the fix.
Check the cold water supply
A combi heats mains water as it passes through, so it needs a good cold supply to work. Run a cold tap in the kitchen. If the flow is weak or there is none, the problem is the mains supply or the stopcock, not the boiler. If no water at all comes out of the hot tap while the cold works, see our guide to no water coming out of the hot tap.
A combi also needs a minimum flow at the tap before it switches to hot water. A tap opened only a trickle may not be enough to trigger it, so open the hot tap fully when testing. The minimum figure for your boiler is in its installation manual. If hot water comes through but is only lukewarm, the Greenstar i fault finding table suggests reducing the flow at the tap, and our guide to hot water that is not hot enough covers the other causes.
Stand by the boiler while someone opens a hot tap fully. If you hear the fan and burner start within a few seconds, the boiler is detecting the flow. If it stays silent, the flow sensor or the mains supply is the likely problem.
Is it the diverter valve on a Worcester?
It often is, if the heating works normally and the boiler fires when you run a hot tap but the water stays cold. The diverter valve is a motorised valve inside the boiler that sends heated water either to the radiators or to the plate heat exchanger that heats your tap water. If it sticks in the heating position, the heat goes to the radiators every time.
The classic signs are radiators that warm up when you run a hot tap, even with the heating switched off, and hot water that comes and goes. The fault is either the actuator, which is the motor head on top of the valve, or the valve itself sticking with wear or debris. Our guide to diverter valve replacement cost explains the repair and what drives the price.
Flow sensor faults
If the boiler does not react at all when you open a hot tap, the hot water flow sensor may not be detecting the flow. Some engineers call it a turbine. Debris or scale can stop it turning, or it can fail electrically. An engineer can test it and clean or replace it.
Scale in the plate heat exchanger
In hard water areas, scale can build up in the plate heat exchanger. That usually gives lukewarm or fluctuating hot water rather than none at all, and it is covered in the guide to hot water that is not hot enough.
How do I reset my Worcester boiler for hot water?
Only reset a Worcester boiler if the display shows a fault code or the blue light is flashing. Press the reset button once on dial and display models, or use the key combination on a Greenstar 4000 or 8000. Our guide to resetting a Worcester boiler shows where the control is on each model.
A reset clears a lockout, so it can bring back the hot water if a brief gas or pressure problem caused the shutdown. It will not free a stuck diverter valve or fix a flow sensor, and there is no separate reset for the hot water alone.
Do not remove the boiler casing to look at the diverter valve or flow sensor. They sit next to the gas valve and electrical parts, and only a Gas Safe registered engineer should work on them. Take care when testing a hot tap after a repair or a change of setting, as water at 60 °C can scald.
When to call an engineer
Call a Gas Safe registered engineer, or Worcester Bosch if the boiler is under guarantee, if the setting is correct, there is no fault code, the pressure is between 1 and 1.5 bar and the mains supply is good, but the taps still run cold. Tell them whether the heating works, whether the boiler fires when you run a hot tap and whether the radiators warm up at the same time. Those three answers usually point straight to the diverter valve or the flow sensor.
For the same symptoms on any make, our guide to no hot water when the heating works covers combi and cylinder systems in general.