Worcester Boiler No Hot Water: What to Check First

Updated July 2026 · Emergency Plumber Chelsea

Start by working out whether you have a combi or a system boiler. A combi, such as most Greenstar i, Si and 4000 and 8000 combis, heats water instantly when you open a tap and has no hot water cylinder. A system or regular boiler heats a cylinder of stored water, usually in an airing cupboard, and the boiler itself does not know a tap has been opened. The checks are different for each, so it is worth confirming before you go further. If you have a cylinder, jump to the section on system boilers below.

Check the display and the gauge first. A code on the screen, or a flashing light on older models, means the boiler has locked out, and it will not give you heating or hot water until the fault is cleared. Write the code down before pressing anything. CE 207 means low system pressure, and topping up to about 1 to 1.5 bar through the filling loop usually brings hot water back. EA 227 means the boiler tried to light and could not detect a flame. Our guide to Worcester boiler fault codes explains the common ones and the checks for each.

If there is no code, make sure the basics are right. Check the hot water temperature control has not been turned down, which is easy to do by accident when cleaning. Open a hot tap fully: a combi needs a minimum flow rate before it fires, so a mixer tap only slightly open, or a tap with a blocked aerator, may not be enough to start the burner. Try another hot tap in the property. If one tap is hot and another is not, the problem is in that tap or its pipework, not the boiler. Many Greenstar combis also have an eco button. With eco switched on, the boiler does not keep its internal store warm, so hot water takes a little longer to arrive. That is normal, not a fault.

Heating working but no hot water is the most common Worcester complaint, and on a combi it usually comes down to two parts. The diverter valve decides whether hot water from the burner goes to the radiators or to the taps. If it sticks in the heating position, the radiators get hot and the taps stay cold. The flow sensor tells the boiler a hot tap has been opened. If it fails, or its small turbine jams with debris, the boiler never realises you want hot water and the burner does not come on. Both are internal parts, so this is an engineer's job. Our guide on a boiler not heating water explains how an engineer tells the two apart.

Lukewarm water that has got gradually worse is usually limescale. London water is hard, and in a combi the mains water passes through a small plate heat exchanger where it picks up heat from the boiler. Scale builds up on the water side of that exchanger over the years, reducing how much heat it can transfer. You notice it first in winter, when the incoming water is colder, and in showers, which need a steady flow at a high temperature. Depending on how badly scaled it is, the exchanger can sometimes be descaled, but it is often simpler to replace it. Our guide to hard water and limescale in London covers ways of protecting a new one.

If you have no hot water and no heating, look beyond the boiler. Check other gas appliances: if the hob will not light, the problem is the gas supply, and on a prepayment meter it may simply be credit. Check the electrical spur that feeds the boiler has not tripped or been switched off. In freezing weather, check the plastic condensate pipe that runs outside from the boiler, because a frozen condensate pipe is one of the main reasons a Worcester boiler locks out on a cold morning. Our frozen condensate pipe guide explains how to thaw it safely with warm water.

On a Worcester system or regular boiler, the fault is often outside the boiler. Check the programmer or timer has the hot water channel switched on, and that the clock is right after a power cut. Check the thermostat on the cylinder, usually a small dial strapped to its side, is set at around 60°C. If the heating works but the cylinder stays cold, a motorised zone valve that has stuck shut is a common cause. These valves have a manual lever on the head, and if moving it brings hot water back, the valve's motor or its wiring has probably failed. If the cylinder has an immersion heater, switching that on gives you hot water while you wait for a repair. Our guide to an immersion heater that is not working covers that side of the system.

Some things are better left alone. Do not take the front casing off the boiler, do not tap the diverter valve housing to free it, and do not keep pressing reset if a code returns straight away. Every failed ignition attempt releases gas that is not burned. If you smell gas at any point, leave the property without using switches and call the National Gas Emergency Service on 0800 111 999 from outside.

Regular servicing prevents some of these faults. During an annual service the engineer checks the condensate trap, the ignition electrode, the pressure and the expansion vessel, and can spot a hot water flow or temperature problem before it becomes a breakdown. Our boiler service covers Worcester Bosch boilers across SW3 and SW10. If your Greenstar is getting on and faults are becoming regular, our guide on when to replace a boiler will help you weigh up repair against replacement.

If your Worcester boiler is still giving no hot water after those checks, call Emergency Plumber Chelsea on 020 3002 6667. Tell us the model from the front panel, any code on the display, whether the heating works and whether you have gas at the hob, and we can often narrow the fault down before an engineer arrives. Our Gas Safe registered engineers carry out boiler repairs in Chelsea, Knightsbridge, Sloane Square, South Kensington and Fulham. We agree the work before we start, and there is no call-out fee on jobs over 3 hours.

Quick tips

• Write down any code on the display before pressing reset.
• Check the pressure gauge: about 1 to 1.5 bar cold is normal on a Greenstar.
• Open the hot tap fully; a combi needs a minimum flow before it fires.
• Heating on but taps cold on a combi usually means the diverter valve or flow sensor.
• On a system boiler, check the programmer's hot water channel and the cylinder thermostat first.

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