Find your model and its controls
Turning on the heating on a Worcester boiler is a two-part job: the boiler must have heating mode switched on, and your programmer and room thermostat must be calling for heat. The buttons differ between ranges, so check the model name printed on the front panel first.
| Model | Heating control on the boiler | Flow temperature range |
|---|---|---|
| Greenstar i (25i, 30i ErP) | Central heating up and down buttons, confirm with OK or wait 4 seconds | Set on the display; an economic setting suits most systems |
| Greenstar 4000 | Heating key switches heating mode on or off, arrow keys set the temperature | 30°C to 82°C, saved after 2 seconds |
| Greenstar 8000 Life | Heating key, navigation keys to adjust | 30°C to 88°C |
| Greenstar 8000+ and 8000+ Style | Heating key, confirm with ok; Heating mode menu offers On, Off, Auto and Once | 30°C to 88°C, saved with ok or after 2 seconds |
These details come from the Worcester Bosch user instructions for each range: the Greenstar i ErP combi (6 720 806 946), the Greenstar 4000 (6 720 891 170), the Greenstar 8000 Life combi (6720883872) and the Greenstar 8000+ (6721890748). If you have an older or different model, download its user instructions from the Worcester Bosch website using the name on the front.
Before you start: power and pressure
The basic checks in the Greenstar 4000 user instructions begin with a simple question: is the electrical power switched on to the boiler? A Worcester boiler is usually powered through a fused spur, a switched socket-style plate on the wall near it. If the display is blank, check that switch, the fuse in it and your consumer unit. None of the 4000 or 8000 manuals describe a separate power button on the boiler itself.
Next, look at the pressure. With the system cold, the 8000 Life and 8000+ user instructions ask for 1 to 1.5 bar and a top up if the reading is below 1 bar. The Greenstar 4000 instructions use a slightly wider band and say to recharge below 0.8 bar, and they colour the reading green for normal, yellow for low or slightly high and red for too low or too high. A boiler with low pressure will not run the heating, so top up first using our Worcester boiler pressure guide.
Step by step: turning the heating on
- Power on. Switch on the fused spur and wait for the display to show the flow temperature.
- Heating mode on. On a 4000, 8000 Life or 8000+, press the heating key. On an 8000+ you can also open the menu, choose Heating mode and select On (always on) or Auto (follow the time programme). Once runs the heating from the first programmed on time to the last off time.
- Set the flow temperature. Use the arrow or navigation keys. The 8000 Life manual suggests about 65°C for radiators and about 50°C for underfloor heating as a starting point.
- Set the programmer or timer. It needs to be on, or in a heating period. A timer set to off will keep the boiler idle however high the boiler setting is.
- Turn up the room thermostat. Set it a few degrees above the current room temperature so it calls for heat.
- Open the radiator valves. Thermostatic radiator valves (TRVs) turned to 0 or the frost setting will keep those radiators cold.
Within a few minutes the burner symbol should appear and the radiators should start to warm from the top.
Heating, hot water and temperature settings
The heating key and the hot water key are separate. On the 8000 Life the hot water temperature can be set from 35°C to 60°C, and on all three newer ranges Eco mode switches off the preheat function to save energy. Eco mode affects how quickly hot water arrives, not whether the heating runs.
The flow temperature you set on the boiler is the maximum temperature of the water sent to the radiators. It is not the room temperature. The Greenstar i manual says that if the house is not reaching the temperature you want, you should use the room thermostat to adjust it. Raising the flow temperature heats radiators faster but reduces how much a condensing boiler condenses.
None of these manuals describe a summer or winter switch. On the Greenstar i, Worcester's advice for summer is to set the programmer to off or turn the room thermostat down to minimum, which leaves hot water working on a combi. On a 4000, 8000 Life or 8000+ you can also switch heating mode off with the heating key, and the 8000+ shows a central heating off symbol when you do.
Thermostats, smart controls and wireless stats
The Greenstar i user instructions state that a room thermostat or programmer must be fitted to control the central heating. In practice the boiler's own settings say how hot the water can get, and the external control decides when heat is needed.
If you have a Worcester Bosch smart control, a Key accessory or another brand's wireless thermostat, check its schedule and any holiday or away setting, and replace the batteries in wireless room units. The 8000 Life display shows Wi-Fi and RF symbols when those accessories are connected. Our guide to a boiler not responding to the thermostat covers controls faults in more detail.
If the heating will not come on
Work through these before calling anyone:
- Fault code or alert: read the code on the display. A Greenstar i also flashes its blue light for a fault. Our Worcester display symbols guide explains what each icon means.
- Gas: check another gas appliance works and that a prepayment meter has credit. If you smell gas, call the National Gas Emergency Service on 0800 111 999.
- Frozen condensate pipe: in a frost, thaw the outside pipe with warm water or a hot water bottle.
- Reset: once the cause is dealt with, reset the boiler once; our Worcester boiler reset guide shows how for each range.
If it still will not run after two or three resets, call a Gas Safe registered engineer. An engineer call-out and diagnosis typically costs £60 to £150.
Some older Worcester manuals describe lighting a pilot flame at the gas valve. Do not attempt this: if an older pilot-light boiler will not light, call a Gas Safe registered engineer. Overheat thermostat reset buttons inside the casing are also for engineers only.
Frost protection and turning the heating off
Worcester's advice for winter is not to switch the boiler off at all. The 4000, 8000 Life and 8000+ user instructions ask you to keep the heating in constant use when there is a risk of frost and, if the home will be empty, to leave the external programmer on constant with the room thermostat at 12°C. The Greenstar i manual suggests 15°C for the same situation and adds that below 8°C the pump will run to circulate water and stop the system freezing, which only works if you do not switch the boiler off at the fused spur.
For summer, turn the heating off at the programmer, the room thermostat or the heating key, and leave the power on so frost protection and hot water keep working.