Worcester boiler no hot water: causes and what to check

First, what is the boiler doing?

Worcester Greenstar combis heat water on demand. When you open a hot tap, water flowing through the boiler is detected, the burner lights and heat is sent to the hot water side instead of the radiators. Anything that breaks that chain gives you cold taps, so the quickest way to narrow it down is to notice what the boiler does when you open a hot tap.

Stand by the boiler with someone running a hot tap. Listen for the fan starting and the burner lighting, and watch the display for a tap symbol, a flame symbol or a fault code. Write down any code exactly as shown, including the number after the letters on models that display both. That single detail often saves a return visit.

Checks you can safely make yourself

These checks do not involve opening the boiler case and are worth doing before you book anyone. A good share of no hot water calls turn out to be pressure, gas supply or a frozen condensate pipe.

• Pressure: the gauge should read about 1 to 1.5 bar when cold. Many Worcester combis will not fire below their minimum. Top up through the filling loop following your manual, and close it fully afterwards.
• Gas: check the hob lights and, on a prepayment meter, that there is credit. If nothing gas-fired works, the problem is the supply rather than the boiler.
• Hot water temperature: make sure the hot water setting on the control panel has not been turned right down.
• Power: if the display is blank, check the fused spur switch next to the boiler and your consumer unit.
• Reset: if the display shows a lockout, press reset once as your manual describes. If it locks out again, stop there and book an engineer.
• Other taps: try the kitchen tap as well as the bathroom. If only one outlet is cold, the fault is at that tap or shower, not the boiler.

Do not remove the boiler casing or try to free internal parts. Work inside a gas appliance must be done by a Gas Safe registered engineer. If you smell gas, turn off the supply at the meter if it is safe to do so, open windows and call the National Gas Emergency Service on 0800 111 999.

Frozen condensate pipe in cold weather

Greenstar boilers are condensing boilers, and they drain acidic condensate water through a plastic pipe, often running outside to a drain. In a hard frost that pipe can freeze. The condensate then backs up inside the boiler, which shuts itself down and shows a fault. You lose both heating and hot water, usually on the coldest morning of the year.

Worcester publishes guidance on thawing the pipe by pouring warm, not boiling, water along the outside section or holding a warm pack against it, then resetting the boiler. Only do this where the pipe is at ground level and safe to reach. If the pipe runs high up a wall, or it freezes every winter, it may need rerouting or insulating. Our guide to boiler condensate pipe routing explains what a good installation looks like.

Heating works but the taps are cold

If the radiators heat up normally but the boiler ignores a running hot tap, the boiler is healthy enough to fire, so attention moves to the parts that switch it into hot water mode. The flow sensor, sometimes called a turbine or flow switch, tells the boiler that a tap is open. If it sticks or fails, the boiler never knows you want hot water.

The diverter valve then sends heat to the hot water side. If it sticks in the heating position, the boiler may fire when you open a tap but send the heat to the radiators instead, so you may notice radiators warming while the tap stays cold. Both parts sit inside the boiler and the correct replacement depends on the exact model, so an engineer should test them before ordering anything. Our general guide to no hot water but heating works covers the same symptom on other makes of boiler.

Lukewarm water and London's hard water

Much of London has hard water, and limescale builds up inside the plate heat exchanger that transfers heat into your tap water. As the scale thickens, the boiler struggles to pass enough heat across, so the water comes out warm rather than hot, or only hot at a very low flow. The heating is often unaffected.

A scaled plate heat exchanger can sometimes be cleaned, but on older boilers replacement is often the more reliable fix. If scale is the cause, it is worth asking about a scale reducer on the incoming cold supply so the new part does not go the same way. Lukewarm water can also come from a partly stuck diverter valve, so diagnosis matters before parts are bought.

Fault codes that stop hot water

Any lockout stops hot water as well as heating. On many Greenstar models an EA code relates to the flame not being detected, and an E9 code relates to an overheat safety device. The number shown alongside the letters matters, because the same letters can have different meanings depending on the model. Our guides to the Worcester Bosch EA fault and the Worcester Bosch E9 fault explain what to record and why.

Pressing reset once to clear a one-off lockout is reasonable. Resetting it again and again is not a fix, and some faults behind a lockout, such as a gas pressure or flue problem, need checking before the boiler is used normally.

If you have a Vaillant rather than a Worcester, our guide to a Vaillant boiler no hot water covers its codes and checks.

Getting hot water back

If the checks above have not brought the hot water back, book a boiler engineer. Tell us the boiler model from the front label or the data plate under the case, any fault code, the pressure reading, whether the heating still works and whether the problem came on suddenly or has been getting worse. That lets the engineer arrive with a sensible idea of the likely part.

Loyal Plumbers runs 10 vans across London and everywhere inside the M25, 24 hours a day, and all gas work is done by Gas Safe registered engineers. Call or send an enquiry and we will diagnose the fault before recommending a repair. If the boiler is old and parts are hard to get, the engineer will say so plainly, and our guide on whether to repair or replace a boiler covers that decision.